diff --git a/ext/openssl/ossl.c b/ext/openssl/ossl.c
index 60780790b..d148447dd 100644
--- a/ext/openssl/ossl.c
+++ b/ext/openssl/ossl.c
@@ -1033,6 +1033,7 @@ Init_openssl(void)
      * Init components
      */
     Init_ossl_asn1();
+    Init_ossl_bio();
     Init_ossl_bn();
     Init_ossl_cipher();
     Init_ossl_config();
diff --git a/ext/openssl/ossl_bio.c b/ext/openssl/ossl_bio.c
index 2ef208050..aad7a4908 100644
--- a/ext/openssl/ossl_bio.c
+++ b/ext/openssl/ossl_bio.c
@@ -40,3 +40,324 @@ ossl_membio2str(BIO *bio)
 
     return ret;
 }
+
+static BIO_METHOD *ossl_bio_meth;
+static VALUE nonblock_kwargs, sym_wait_readable, sym_wait_writable;
+
+struct ossl_bio_ctx {
+    VALUE io;
+    int state;
+    int eof;
+};
+
+static void
+bio_free(void *ptr)
+{
+    BIO_free(ptr);
+}
+
+static void
+bio_mark(void *ptr)
+{
+    struct ossl_bio_ctx *ctx = BIO_get_data(ptr);
+    rb_gc_mark_movable(ctx->io);
+}
+
+static void
+bio_compact(void *ptr)
+{
+    struct ossl_bio_ctx *ctx = BIO_get_data(ptr);
+    ctx->io = rb_gc_location(ctx->io);
+}
+
+static const rb_data_type_t ossl_bio_type = {
+    "OpenSSL/BIO",
+    {
+        .dmark = bio_mark,
+        .dfree = bio_free,
+        .dcompact = bio_compact,
+    },
+    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED,
+};
+
+VALUE
+ossl_bio_new(VALUE io)
+{
+    VALUE obj = TypedData_Wrap_Struct(rb_cObject, &ossl_bio_type, NULL);
+    BIO *bio = BIO_new(ossl_bio_meth);
+    if (!bio)
+        ossl_raise(eOSSLError, "BIO_new");
+
+    struct ossl_bio_ctx *ctx = BIO_get_data(bio);
+    ctx->io = io;
+    BIO_set_init(bio, 1);
+    RTYPEDDATA_DATA(obj) = bio;
+    return obj;
+}
+
+BIO *
+ossl_bio_get(VALUE obj)
+{
+    BIO *bio;
+    TypedData_Get_Struct(obj, BIO, &ossl_bio_type, bio);
+    return bio;
+}
+
+int
+ossl_bio_state(VALUE obj)
+{
+    BIO *bio;
+    TypedData_Get_Struct(obj, BIO, &ossl_bio_type, bio);
+
+    struct ossl_bio_ctx *ctx = BIO_get_data(bio);
+    int state = ctx->state;
+    ctx->state = 0;
+    return state;
+}
+
+static int
+bio_create(BIO *bio)
+{
+    struct ossl_bio_ctx *ctx = OPENSSL_malloc(sizeof(*ctx));
+    if (!ctx)
+        return 0;
+    memset(ctx, 0, sizeof(*ctx));
+    BIO_set_data(bio, ctx);
+
+    return 1;
+}
+
+static int
+bio_destroy(BIO *bio)
+{
+    struct ossl_bio_ctx *ctx = BIO_get_data(bio);
+    if (ctx) {
+        OPENSSL_free(ctx);
+        BIO_set_data(bio, NULL);
+    }
+
+    return 1;
+}
+
+struct bwrite_args {
+    BIO *bio;
+    struct ossl_bio_ctx *ctx;
+    const char *data;
+    int dlen;
+    int written;
+};
+
+static VALUE
+bio_bwrite0(VALUE args)
+{
+    struct bwrite_args *p = (void *)args;
+    BIO_clear_retry_flags(p->bio);
+
+    VALUE fargs[] = { rb_str_new_static(p->data, p->dlen), nonblock_kwargs };
+    VALUE ret = rb_funcallv_kw(p->ctx->io, rb_intern("write_nonblock"),
+                               2, fargs, RB_PASS_KEYWORDS);
+
+    if (RB_INTEGER_TYPE_P(ret)) {
+        p->written = NUM2INT(ret);
+        return Qtrue;
+    }
+    else if (ret == sym_wait_readable) {
+        BIO_set_retry_read(p->bio);
+        return Qfalse;
+    }
+    else if (ret == sym_wait_writable) {
+        BIO_set_retry_write(p->bio);
+        return Qfalse;
+    }
+    else {
+        rb_raise(rb_eTypeError, "write_nonblock must return an Integer, "
+                 ":wait_readable, or :wait_writable");
+    }
+}
+
+struct call0_args {
+    VALUE (*func)(VALUE);
+    VALUE args;
+    VALUE ret;
+};
+
+static VALUE
+do_nothing(VALUE _)
+{
+    return Qnil;
+}
+
+static VALUE
+call_protect1(VALUE args_)
+{
+    struct call0_args *args = (void *)args_;
+    rb_set_errinfo(Qnil);
+    args->ret = args->func(args->args);
+    return Qnil;
+}
+
+static VALUE
+call_protect0(VALUE args_)
+{
+    /*
+     * At this point rb_errinfo() may be set by another callback called from
+     * the same OpenSSL function (e.g., SSL_accept()).
+     *
+     * Abusing rb_ensure() to temporarily save errinfo and restore it after
+     * the BIO callback successfully returns.
+     */
+    rb_ensure(do_nothing, Qnil, call_protect1, args_);
+    return Qnil;
+}
+
+static VALUE
+call_protect(VALUE (*func)(VALUE), VALUE args, int *state)
+{
+    /*
+     * FIXME: should check !NIL_P(rb_ivar_get(ssl_obj, ID_callback_state))
+     * instead to see if a tag jump is pending or not.
+     */
+    int pending = !NIL_P(rb_errinfo());
+    struct call0_args call0_args = { func, args, Qfalse };
+    rb_protect(call_protect0, (VALUE)&call0_args, state);
+    if (pending && *state)
+        rb_warn("exception ignored in BIO callback: pending=%d", pending);
+    return call0_args.ret;
+}
+
+static int
+bio_bwrite(BIO *bio, const char *data, int dlen)
+{
+    struct ossl_bio_ctx *ctx = BIO_get_data(bio);
+    struct bwrite_args args = { bio, ctx, data, dlen, 0 };
+    int state;
+
+    if (ctx->state)
+        return -1;
+
+    VALUE ok = call_protect(bio_bwrite0, (VALUE)&args, &state);
+    if (state) {
+        ctx->state = state;
+        return -1;
+    }
+    if (RTEST(ok))
+        return args.written;
+    return -1;
+}
+
+struct bread_args {
+    BIO *bio;
+    struct ossl_bio_ctx *ctx;
+    char *data;
+    int dlen;
+    int readbytes;
+};
+
+static VALUE
+bio_bread0(VALUE args)
+{
+    struct bread_args *p = (void *)args;
+    BIO_clear_retry_flags(p->bio);
+
+    VALUE fargs[] = { INT2NUM(p->dlen), nonblock_kwargs };
+    VALUE ret = rb_funcallv_kw(p->ctx->io, rb_intern("read_nonblock"),
+                               2, fargs, RB_PASS_KEYWORDS);
+
+    if (RB_TYPE_P(ret, T_STRING)) {
+        int len = RSTRING_LENINT(ret);
+        if (len > p->dlen)
+            rb_raise(rb_eTypeError, "read_nonblock returned too much data");
+        memcpy(p->data, RSTRING_PTR(ret), len);
+        p->readbytes = len;
+        return Qtrue;
+    }
+    else if (NIL_P(ret)) {
+        // In OpenSSL 3.0 or later: BIO_set_flags(p->bio, BIO_FLAGS_IN_EOF);
+        p->ctx->eof = 1;
+        return Qtrue;
+    }
+    else if (ret == sym_wait_readable) {
+        BIO_set_retry_read(p->bio);
+        return Qfalse;
+    }
+    else if (ret == sym_wait_writable) {
+        BIO_set_retry_write(p->bio);
+        return Qfalse;
+    }
+    else {
+        rb_raise(rb_eTypeError, "write_nonblock must return an Integer, "
+                 ":wait_readable, or :wait_writable");
+    }
+}
+
+static int
+bio_bread(BIO *bio, char *data, int dlen)
+{
+    struct ossl_bio_ctx *ctx = BIO_get_data(bio);
+    struct bread_args args = { bio, ctx, data, dlen, 0 };
+    int state;
+
+    if (ctx->state)
+        return -1;
+
+    VALUE ok = call_protect(bio_bread0, (VALUE)&args, &state);
+    if (state) {
+        ctx->state = state;
+        return -1;
+    }
+    if (RTEST(ok))
+        return args.readbytes;
+    return -1;
+}
+
+static VALUE
+bio_flush0(VALUE vctx)
+{
+    struct ossl_bio_ctx *ctx = (void *)vctx;
+    return rb_funcallv(ctx->io, rb_intern("flush"), 0, NULL);
+}
+
+static long
+bio_ctrl(BIO *bio, int cmd, long larg, void *parg)
+{
+    struct ossl_bio_ctx *ctx = BIO_get_data(bio);
+    int state;
+
+    if (ctx->state)
+        return 0;
+
+    switch (cmd) {
+      case BIO_CTRL_EOF:
+        return ctx->eof;
+      case BIO_CTRL_FLUSH:
+        call_protect(bio_flush0, (VALUE)ctx, &state);
+        ctx->state = state;
+        return !state;
+      default:
+        return 0;
+    }
+}
+
+void
+Init_ossl_bio(void)
+{
+    ossl_bio_meth = BIO_meth_new(BIO_TYPE_SOURCE_SINK, "Ruby IO-like object");
+    if (!ossl_bio_meth)
+        ossl_raise(eOSSLError, "BIO_meth_new");
+    if (!BIO_meth_set_create(ossl_bio_meth, bio_create) ||
+        !BIO_meth_set_destroy(ossl_bio_meth, bio_destroy) ||
+        !BIO_meth_set_write(ossl_bio_meth, bio_bwrite) ||
+        !BIO_meth_set_read(ossl_bio_meth, bio_bread) ||
+        !BIO_meth_set_ctrl(ossl_bio_meth, bio_ctrl)) {
+        BIO_meth_free(ossl_bio_meth);
+        ossl_bio_meth = NULL;
+        ossl_raise(eOSSLError, "BIO_meth_set_*");
+    }
+
+    nonblock_kwargs = rb_hash_new();
+    rb_hash_aset(nonblock_kwargs, ID2SYM(rb_intern_const("exception")), Qfalse);
+    rb_global_variable(&nonblock_kwargs);
+
+    sym_wait_readable = ID2SYM(rb_intern_const("wait_readable"));
+    sym_wait_writable = ID2SYM(rb_intern_const("wait_writable"));
+}
diff --git a/ext/openssl/ossl_bio.h b/ext/openssl/ossl_bio.h
index 1b871f1cd..634f99fae 100644
--- a/ext/openssl/ossl_bio.h
+++ b/ext/openssl/ossl_bio.h
@@ -13,4 +13,10 @@
 BIO *ossl_obj2bio(volatile VALUE *);
 VALUE ossl_membio2str(BIO*);
 
+VALUE ossl_bio_new(VALUE io);
+BIO *ossl_bio_get(VALUE obj);
+int ossl_bio_state(VALUE obj);
+
+void Init_ossl_bio(void);
+
 #endif
diff --git a/ext/openssl/ossl_ssl.c b/ext/openssl/ossl_ssl.c
index a5b25e14d..3a3fceef1 100644
--- a/ext/openssl/ossl_ssl.c
+++ b/ext/openssl/ossl_ssl.c
@@ -37,7 +37,7 @@ static VALUE eSSLErrorWaitReadable;
 static VALUE eSSLErrorWaitWritable;
 
 static ID id_call, ID_callback_state, id_tmp_dh_callback,
-	  id_npn_protocols_encoded, id_each;
+	  id_npn_protocols_encoded, id_each, id_bio;
 static VALUE sym_exception, sym_wait_readable, sym_wait_writable;
 
 static ID id_i_cert_store, id_i_ca_file, id_i_ca_path, id_i_verify_mode,
@@ -1536,7 +1536,10 @@ ossl_ssl_s_alloc(VALUE klass)
 static VALUE
 peer_ip_address(VALUE self)
 {
-    VALUE remote_address = rb_funcall(rb_attr_get(self, id_i_io), rb_intern("remote_address"), 0);
+    VALUE io = rb_attr_get(self, id_i_io);
+    VALUE remote_address = rb_check_funcall(io, rb_intern("remote_address"), 0, NULL);
+    if (remote_address == Qundef)
+        return rb_str_new_cstr("(unsupported)");
 
     return rb_funcall(remote_address, rb_intern("inspect_sockaddr"), 0);
 }
@@ -1550,10 +1553,16 @@ fallback_peer_ip_address(VALUE self, VALUE args)
 static VALUE
 peeraddr_ip_str(VALUE self)
 {
-    VALUE rb_mErrno = rb_const_get(rb_cObject, rb_intern("Errno"));
-    VALUE rb_eSystemCallError = rb_const_get(rb_mErrno, rb_intern("SystemCallError"));
+    return rb_rescue2(peer_ip_address, self, fallback_peer_ip_address, Qnil,
+                      rb_eSystemCallError, (VALUE)0);
+}
 
-    return rb_rescue2(peer_ip_address, self, fallback_peer_ip_address, (VALUE)0, rb_eSystemCallError, NULL);
+static int
+is_real_socket(VALUE io)
+{
+    // FIXME: DO NOT MERGE
+    return 0;
+    return RB_TYPE_P(io, T_FILE);
 }
 
 /*
@@ -1561,8 +1570,10 @@ peeraddr_ip_str(VALUE self)
  *    SSLSocket.new(io) => aSSLSocket
  *    SSLSocket.new(io, ctx) => aSSLSocket
  *
- * Creates a new SSL socket from _io_ which must be a real IO object (not an
- * IO-like object that responds to read/write).
+ * Creates a new SSL socket from the underlying socket _io_ and _ctx_.
+ *
+ * _io_ must be an IO object, typically a TCPSocket or Socket from the socket
+ * library, or an IO-like object that supports the typical IO methods.
  *
  * If _ctx_ is provided the SSL Sockets initial params will be taken from
  * the context.
@@ -1571,6 +1582,22 @@ peeraddr_ip_str(VALUE self)
  *
  * This method will freeze the SSLContext if one is provided;
  * however, session management is still allowed in the frozen SSLContext.
+ *
+ * == Support for IO-like objects
+ *
+ * Support for IO-like objects was added in version 3.3 and is experimental.
+ *
+ * As of version 3.3, SSLSocket uses the following methods:
+ *
+ * - <tt>write_nonblock</tt> with the <tt>exception: false</tt> option
+ * - <tt>read_nonblock</tt> with the <tt>exception: false</tt> option
+ * - <tt>wait_readable</tt>
+ * - <tt>wait_writable</tt>
+ * - <tt>flush</tt>
+ * - <tt>close</tt>
+ * - <tt>closed?</tt>
+ *
+ * Note that future versions may require additional methods to be implemented.
  */
 static VALUE
 ossl_ssl_initialize(int argc, VALUE *argv, VALUE self)
@@ -1590,9 +1617,18 @@ ossl_ssl_initialize(int argc, VALUE *argv, VALUE self)
     rb_ivar_set(self, id_i_context, v_ctx);
     ossl_sslctx_setup(v_ctx);
 
-    if (rb_respond_to(io, rb_intern("nonblock=")))
-	rb_funcall(io, rb_intern("nonblock="), 1, Qtrue);
-    Check_Type(io, T_FILE);
+    if (is_real_socket(io)) {
+        rb_io_t *fptr;
+        GetOpenFile(io, fptr);
+        rb_io_set_nonblock(fptr);
+    }
+    else {
+        // Not meant to be a comprehensive check
+        if (!rb_respond_to(io, rb_intern("read_nonblock")) ||
+            !rb_respond_to(io, rb_intern("write_nonblock")))
+            rb_raise(rb_eTypeError, "io must be a real IO object or an IO-like "
+                     "object that responds to read_nonblock and write_nonblock");
+    }
     rb_ivar_set(self, id_i_io, io);
 
     ssl = SSL_new(ctx);
@@ -1624,27 +1660,57 @@ ossl_ssl_setup(VALUE self)
 {
     VALUE io;
     SSL *ssl;
-    rb_io_t *fptr;
 
     GetSSL(self, ssl);
     if (ssl_started(ssl))
 	return Qtrue;
 
     io = rb_attr_get(self, id_i_io);
-    GetOpenFile(io, fptr);
-    rb_io_check_readable(fptr);
-    rb_io_check_writable(fptr);
-    if (!SSL_set_fd(ssl, TO_SOCKET(rb_io_descriptor(io))))
-        ossl_raise(eSSLError, "SSL_set_fd");
+    if (is_real_socket(io)) {
+        rb_io_t *fptr;
+        GetOpenFile(io, fptr);
+        rb_io_check_readable(fptr);
+        rb_io_check_writable(fptr);
+        if (!SSL_set_fd(ssl, TO_SOCKET(rb_io_descriptor(io))))
+            ossl_raise(eSSLError, "SSL_set_fd");
+    }
+    else {
+        VALUE bobj = ossl_bio_new(io);
+        rb_ivar_set(self, id_bio, bobj);
+
+        BIO *bio = ossl_bio_get(bobj);
+        if (!BIO_up_ref(bio))
+            ossl_raise(eSSLError, "BIO_up_ref");
+        SSL_set_bio(ssl, bio, bio);
+    }
 
     return Qtrue;
 }
 
+static void
+check_bio_error(VALUE self, SSL *ssl, VALUE bobj, int ret)
+{
+    if (NIL_P(bobj)) {
 #ifdef _WIN32
-#define ssl_get_error(ssl, ret) (errno = rb_w32_map_errno(WSAGetLastError()), SSL_get_error((ssl), (ret)))
-#else
-#define ssl_get_error(ssl, ret) SSL_get_error((ssl), (ret))
+        errno = rb_w32_map_errno(WSAGetLastError());
 #endif
+    }
+    else {
+        int state = ossl_bio_state(bobj);
+        if (state) {
+            ossl_clear_error();
+            rb_jump_tag(state);
+        }
+        errno = 0;
+    }
+
+    VALUE cb_state = rb_attr_get(self, ID_callback_state);
+    if (!NIL_P(cb_state)) {
+        /* must cleanup OpenSSL error stack before re-raising */
+        ossl_clear_error();
+        rb_jump_tag(NUM2INT(cb_state));
+    }
+}
 
 static void
 write_would_block(int nonblock)
@@ -1684,6 +1750,11 @@ no_exception_p(VALUE opts)
 static void
 io_wait_writable(VALUE io)
 {
+    if (!is_real_socket(io)) {
+        if (!RTEST(rb_funcallv(io, rb_intern("wait_writable"), 0, NULL)))
+            rb_raise(IO_TIMEOUT_ERROR, "Timed out while waiting to become writable!");
+        return;
+    }
 #ifdef HAVE_RB_IO_MAYBE_WAIT
     if (!rb_io_maybe_wait_writable(errno, io, RUBY_IO_TIMEOUT_DEFAULT)) {
         rb_raise(IO_TIMEOUT_ERROR, "Timed out while waiting to become writable!");
@@ -1698,6 +1769,11 @@ io_wait_writable(VALUE io)
 static void
 io_wait_readable(VALUE io)
 {
+    if (!is_real_socket(io)) {
+        if (!RTEST(rb_funcallv(io, rb_intern("wait_readable"), 0, NULL)))
+            rb_raise(IO_TIMEOUT_ERROR, "Timed out while waiting to become readable!");
+        return;
+    }
 #ifdef HAVE_RB_IO_MAYBE_WAIT
     if (!rb_io_maybe_wait_readable(errno, io, RUBY_IO_TIMEOUT_DEFAULT)) {
         rb_raise(IO_TIMEOUT_ERROR, "Timed out while waiting to become readable!");
@@ -1714,28 +1790,22 @@ ossl_start_ssl(VALUE self, int (*func)(SSL *), const char *funcname, VALUE opts)
 {
     SSL *ssl;
     int ret, ret2;
-    VALUE cb_state;
     int nonblock = opts != Qfalse;
 
-    rb_ivar_set(self, ID_callback_state, Qnil);
-
     GetSSL(self, ssl);
 
-    VALUE io = rb_attr_get(self, id_i_io);
+    VALUE io = rb_attr_get(self, id_i_io),
+          bobj = rb_attr_get(self, id_bio);
+
+    rb_ivar_set(self, ID_callback_state, Qnil);
     for (;;) {
         ret = func(ssl);
-
-        cb_state = rb_attr_get(self, ID_callback_state);
-        if (!NIL_P(cb_state)) {
-            /* must cleanup OpenSSL error stack before re-raising */
-            ossl_clear_error();
-            rb_jump_tag(NUM2INT(cb_state));
-        }
+        check_bio_error(self, ssl, bobj, ret);
 
         if (ret > 0)
             break;
 
-        switch ((ret2 = ssl_get_error(ssl, ret))) {
+        switch ((ret2 = SSL_get_error(ssl, ret))) {
           case SSL_ERROR_WANT_WRITE:
             if (no_exception_p(opts)) { return sym_wait_writable; }
             write_would_block(nonblock);
@@ -1885,7 +1955,7 @@ ossl_ssl_read_internal(int argc, VALUE *argv, VALUE self, int nonblock)
 {
     SSL *ssl;
     int ilen;
-    VALUE len, str, cb_state;
+    VALUE len, str;
     VALUE opts = Qnil;
 
     if (nonblock) {
@@ -1913,21 +1983,17 @@ ossl_ssl_read_internal(int argc, VALUE *argv, VALUE self, int nonblock)
         return str;
     }
 
-    VALUE io = rb_attr_get(self, id_i_io);
+    VALUE io = rb_attr_get(self, id_i_io),
+          bobj = rb_attr_get(self, id_bio);
 
+    rb_ivar_set(self, ID_callback_state, Qnil);
     for (;;) {
         rb_str_locktmp(str);
         int nread = SSL_read(ssl, RSTRING_PTR(str), ilen);
         rb_str_unlocktmp(str);
+        check_bio_error(self, ssl, bobj, nread);
 
-        cb_state = rb_attr_get(self, ID_callback_state);
-        if (!NIL_P(cb_state)) {
-            rb_ivar_set(self, ID_callback_state, Qnil);
-            ossl_clear_error();
-            rb_jump_tag(NUM2INT(cb_state));
-        }
-
-        switch (ssl_get_error(ssl, nread)) {
+        switch (SSL_get_error(ssl, nread)) {
           case SSL_ERROR_NONE:
             rb_str_set_len(str, nread);
             return str;
@@ -2018,33 +2084,26 @@ ossl_ssl_write_internal_safe(VALUE _args)
     VALUE opts = args[2];
 
     SSL *ssl;
-    rb_io_t *fptr;
     int num, nonblock = opts != Qfalse;
-    VALUE cb_state;
 
     GetSSL(self, ssl);
     if (!ssl_started(ssl))
         rb_raise(eSSLError, "SSL session is not started yet");
 
-    VALUE io = rb_attr_get(self, id_i_io);
-    GetOpenFile(io, fptr);
-
     /* SSL_write(3ssl) manpage states num == 0 is undefined */
     num = RSTRING_LENINT(str);
     if (num == 0)
         return INT2FIX(0);
 
+    VALUE io = rb_attr_get(self, id_i_io),
+          bobj = rb_attr_get(self, id_bio);
+
+    rb_ivar_set(self, ID_callback_state, Qnil);
     for (;;) {
         int nwritten = SSL_write(ssl, RSTRING_PTR(str), num);
+        check_bio_error(self, ssl, bobj, nwritten);
 
-        cb_state = rb_attr_get(self, ID_callback_state);
-        if (!NIL_P(cb_state)) {
-            rb_ivar_set(self, ID_callback_state, Qnil);
-            ossl_clear_error();
-            rb_jump_tag(NUM2INT(cb_state));
-        }
-
-        switch (ssl_get_error(ssl, nwritten)) {
+        switch (SSL_get_error(ssl, nwritten)) {
           case SSL_ERROR_NONE:
             return INT2NUM(nwritten);
           case SSL_ERROR_WANT_WRITE:
@@ -2143,7 +2202,14 @@ ossl_ssl_stop(VALUE self)
     GetSSL(self, ssl);
     if (!ssl_started(ssl))
 	return Qnil;
+
     ret = SSL_shutdown(ssl);
+
+    /* XXX: Suppressing errors from the underlying socket */
+    VALUE bobj = rb_attr_get(self, id_bio);
+    if (!NIL_P(bobj) && ossl_bio_state(bobj))
+        rb_set_errinfo(Qnil);
+
     if (ret == 1) /* Have already received close_notify */
 	return Qnil;
     if (ret == 0) /* Sent close_notify, but we don't wait for reply */
@@ -3121,6 +3187,7 @@ Init_ossl_ssl(void)
     id_tmp_dh_callback = rb_intern_const("tmp_dh_callback");
     id_npn_protocols_encoded = rb_intern_const("npn_protocols_encoded");
     id_each = rb_intern_const("each");
+    id_bio = rb_intern_const("bio");
 
 #define DefIVarID(name) do \
     id_i_##name = rb_intern_const("@"#name); while (0)
diff --git a/lib/openssl/buffering.rb b/lib/openssl/buffering.rb
index 1464a4292..aa39105f9 100644
--- a/lib/openssl/buffering.rb
+++ b/lib/openssl/buffering.rb
@@ -60,7 +60,7 @@ def initialize(*)
     super
     @eof = false
     @rbuffer = Buffer.new
-    @sync = @io.sync
+    @sync = @io.respond_to?(:sync) ? @io.sync : true
   end
 
   #
diff --git a/test/openssl/test_pair.rb b/test/openssl/test_pair.rb
index 10942191d..1664c00c8 100644
--- a/test/openssl/test_pair.rb
+++ b/test/openssl/test_pair.rb
@@ -67,6 +67,32 @@ def create_tcp_client(host, port)
   end
 end
 
+module OpenSSL::SSLPairIOish
+  include OpenSSL::SSLPairM
+
+  def create_tcp_server(host, port)
+    Addrinfo.tcp(host, port).listen
+  end
+
+  class TCPSocketWrapper
+    def initialize(io) @io = io end
+    def read_nonblock(*args, **kwargs) @io.read_nonblock(*args, **kwargs) end
+    def write_nonblock(*args, **kwargs) @io.write_nonblock(*args, **kwargs) end
+    def wait_readable() @io.wait_readable end
+    def wait_writable() @io.wait_writable end
+    def flush() @io.flush end
+    def close() @io.close end
+    def closed?() @io.closed? end
+
+    # Only used within test_pair.rb
+    def write(*args) @io.write(*args) end
+  end
+
+  def create_tcp_client(host, port)
+    TCPSocketWrapper.new(Addrinfo.tcp(host, port).connect)
+  end
+end
+
 module OpenSSL::TestEOF1M
   def open_file(content)
     ssl_pair { |s1, s2|
@@ -518,6 +544,12 @@ class OpenSSL::TestEOF1LowlevelSocket < OpenSSL::TestCase
   include OpenSSL::TestEOF1M
 end
 
+class OpenSSL::TestEOF1IOish < OpenSSL::TestCase
+  include OpenSSL::TestEOF
+  include OpenSSL::SSLPairIOish
+  include OpenSSL::TestEOF1M
+end
+
 class OpenSSL::TestEOF2 < OpenSSL::TestCase
   include OpenSSL::TestEOF
   include OpenSSL::SSLPair
@@ -530,6 +562,12 @@ class OpenSSL::TestEOF2LowlevelSocket < OpenSSL::TestCase
   include OpenSSL::TestEOF2M
 end
 
+class OpenSSL::TestEOF2IOish < OpenSSL::TestCase
+  include OpenSSL::TestEOF
+  include OpenSSL::SSLPairIOish
+  include OpenSSL::TestEOF2M
+end
+
 class OpenSSL::TestPair < OpenSSL::TestCase
   include OpenSSL::SSLPair
   include OpenSSL::TestPairM
@@ -540,4 +578,9 @@ class OpenSSL::TestPairLowlevelSocket < OpenSSL::TestCase
   include OpenSSL::TestPairM
 end
 
+class OpenSSL::TestPairIOish < OpenSSL::TestCase
+  include OpenSSL::SSLPairIOish
+  include OpenSSL::TestPairM
+end
+
 end
diff --git a/test/openssl/test_ssl.rb b/test/openssl/test_ssl.rb
index 4642063f4..a5e0c0443 100644
--- a/test/openssl/test_ssl.rb
+++ b/test/openssl/test_ssl.rb
@@ -4,17 +4,6 @@
 if defined?(OpenSSL::SSL)
 
 class OpenSSL::TestSSL < OpenSSL::SSLTestCase
-  def test_bad_socket
-    bad_socket = Struct.new(:sync).new
-    assert_raise TypeError do
-      socket = OpenSSL::SSL::SSLSocket.new bad_socket
-      # if the socket is not a T_FILE, `connect` will segv because it tries
-      # to get the underlying file descriptor but the API it calls assumes
-      # the object type is T_FILE
-      socket.connect
-    end
-  end
-
   def test_ctx_setup
     ctx = OpenSSL::SSL::SSLContext.new
     assert_equal true, ctx.setup
@@ -170,6 +159,155 @@ def test_socket_close_write
     end
   end
 
+  def test_synthetic_io_sanity_check
+    obj = Object.new
+    assert_raise_with_message(TypeError, /read_nonblock/) { OpenSSL::SSL::SSLSocket.new(obj) }
+
+    obj = Object.new
+    obj.define_singleton_method(:read_nonblock) { |*args, **kwargs| }
+    obj.define_singleton_method(:write_nonblock) { |*args, **kwargs| }
+    assert_nothing_raised { OpenSSL::SSL::SSLSocket.new(obj) }
+  end
+
+  def test_synthetic_io
+    start_server do |port|
+      tcp = TCPSocket.new("127.0.0.1", port)
+      obj = Object.new
+      obj.define_singleton_method(:read_nonblock) { |maxlen, exception:|
+        tcp.read_nonblock(maxlen, exception: exception) }
+      obj.define_singleton_method(:write_nonblock) { |str, exception:|
+        tcp.write_nonblock(str, exception: exception) }
+      obj.define_singleton_method(:wait_readable) { tcp.wait_readable }
+      obj.define_singleton_method(:wait_writable) { tcp.wait_writable }
+      obj.define_singleton_method(:flush) { tcp.flush }
+      obj.define_singleton_method(:closed?) { tcp.closed? }
+
+      ssl = OpenSSL::SSL::SSLSocket.new(obj)
+      assert_same obj, ssl.to_io
+
+      ssl.connect
+      ssl.puts "abc"; assert_equal "abc\n", ssl.gets
+    ensure
+      ssl&.close
+      tcp&.close
+    end
+  end
+
+  def test_synthetic_io_write_nonblock_exception
+    start_server(ignore_listener_error: true) do |port|
+      tcp = TCPSocket.new("127.0.0.1", port)
+      obj = Object.new
+      [:read_nonblock, :wait_readable, :wait_writable, :flush, :closed?].each do |name|
+        obj.define_singleton_method(name) { |*args, **kwargs|
+          tcp.__send__(name, *args, **kwargs) }
+      end
+
+      # SSLSocket#connect calls write_nonblock at least twice: to write
+      # ClientHello and Finished. Let's raise an exception in the 2nd call.
+      called = 0
+      obj.define_singleton_method(:write_nonblock) { |*args, **kwargs|
+        raise "foo" if (called += 1) == 2
+        tcp.write_nonblock(*args, **kwargs)
+      }
+
+      ssl = OpenSSL::SSL::SSLSocket.new(obj)
+      assert_raise_with_message(RuntimeError, "foo") { ssl.connect }
+    ensure
+      ssl&.close
+      tcp&.close
+    end
+  end
+
+  def test_synthetic_io_errors_in_servername_cb
+    assert_separately(["-ropenssl"], <<~"end;")
+  begin
+    #sock1, sock2 = socketpair
+    sock1, sock2 = if defined? UNIXSocket
+      UNIXSocket.pair
+    else
+      Socket.pair(Socket::AF_INET, Socket::SOCK_STREAM, 0)
+    end
+
+    t = Thread.new {
+      s1 = OpenSSL::SSL::SSLSocket.new(sock1)
+      s1.hostname = "localhost"
+      assert_raise_with_message(OpenSSL::SSL::SSLError, /unrecognized.name/i) {
+        s1.connect
+      }
+    }
+
+    ctx2 = OpenSSL::SSL::SSLContext.new
+    ctx2.servername_cb = lambda { |args| raise RuntimeError, "exc in servername_cb" }
+    obj = Object.new
+    obj.define_singleton_method(:method_missing) { |name, *args, **kwargs| sock2.__send__(name, *args, **kwargs) }
+    obj.define_singleton_method(:respond_to_missing?) { |name, *args, **kwargs| sock2.respond_to?(name, *args, **kwargs) }
+    obj.define_singleton_method(:write_nonblock) { |*args, **kwargs|
+      begin
+        raise "exc in write_nonblock"
+      rescue
+        p $!
+      end
+      p $!
+      sock2.write_nonblock(*args, **kwargs)
+    }
+    s2 = OpenSSL::SSL::SSLSocket.new(obj, ctx2)
+    assert_raise_with_message(RuntimeError, "exc in servername_cb") { s2.accept }
+    assert t.join
+  ensure
+    sock1.close
+    sock2.close
+  end
+    end;
+  end
+
+  def test_synthetic_io_errors_in_callback_and_socket
+    assert_separately(["-ropenssl"], <<~"end;", ignore_stderr: true)
+  begin
+    #sock1, sock2 = socketpair
+    sock1, sock2 = if defined? UNIXSocket
+      UNIXSocket.pair
+    else
+      Socket.pair(Socket::AF_INET, Socket::SOCK_STREAM, 0)
+    end
+
+    t = Thread.new {
+      s1 = OpenSSL::SSL::SSLSocket.new(sock1)
+      s1.hostname = "localhost"
+      begin
+        s1.connect
+      rescue
+      end
+    }
+
+    called = []
+    ctx2 = OpenSSL::SSL::SSLContext.new
+    ctx2.servername_cb = lambda { |args|
+      called << :servername_cb
+      raise "servername_cb"
+    }
+    obj = Object.new
+    obj.define_singleton_method(:method_missing) { |name, *args, **kwargs| sock2.__send__(name, *args, **kwargs) }
+    obj.define_singleton_method(:respond_to_missing?) { |name, *args, **kwargs| sock2.respond_to?(name, *args, **kwargs) }
+    obj.define_singleton_method(:write_nonblock) { |*args, **kwargs|
+      called << :write_nonblock
+      throw :throw_from, :write_nonblock
+    }
+    s2 = OpenSSL::SSL::SSLSocket.new(obj, ctx2)
+
+    ret = assert_warning(/exception ignored/) {
+      catch(:throw_from) { s2.accept }
+    }
+    assert_equal(:write_nonblock, ret)
+    assert_equal([:servername_cb, :write_nonblock], called)
+    sock2.close
+    assert t.join
+  ensure
+    sock1.close
+    sock2.close
+  end
+    end;
+  end
+
   def test_add_certificate
     ctx_proc = -> ctx {
       # Unset values set by start_server
@@ -1062,36 +1200,44 @@ def test_tlsext_hostname
     end
   end
 
-  def test_servername_cb_raises_an_exception_on_unknown_objects
-    hostname = 'example.org'
-
-    ctx2 = OpenSSL::SSL::SSLContext.new
-    ctx2.cert = @svr_cert
-    ctx2.key = @svr_key
-    ctx2.servername_cb = lambda { |args| Object.new }
-
+  def test_servername_cb_exception
     sock1, sock2 = socketpair
 
+    t = Thread.new {
+      s1 = OpenSSL::SSL::SSLSocket.new(sock1)
+      s1.hostname = "localhost"
+      assert_raise_with_message(OpenSSL::SSL::SSLError, /unrecognized.name/i) {
+        s1.connect
+      }
+    }
+
+    ctx2 = OpenSSL::SSL::SSLContext.new
+    ctx2.servername_cb = lambda { |args| raise RuntimeError, "foo" }
     s2 = OpenSSL::SSL::SSLSocket.new(sock2, ctx2)
+    assert_raise_with_message(RuntimeError, "foo") { s2.accept }
+    assert t.join
+  ensure
+    sock1.close
+    sock2.close
+  end
 
-    ctx1 = OpenSSL::SSL::SSLContext.new
+  def test_servername_cb_raises_an_exception_on_unknown_objects
+    sock1, sock2 = socketpair
 
-    s1 = OpenSSL::SSL::SSLSocket.new(sock1, ctx1)
-    s1.hostname = hostname
     t = Thread.new {
-      assert_raise(OpenSSL::SSL::SSLError) do
-        s1.connect
-      end
+      s1 = OpenSSL::SSL::SSLSocket.new(sock1)
+      s1.hostname = "localhost"
+      assert_raise(OpenSSL::SSL::SSLError) { s1.connect }
     }
 
-    assert_raise(ArgumentError) do
-      s2.accept
-    end
-
+    ctx2 = OpenSSL::SSL::SSLContext.new
+    ctx2.servername_cb = lambda { |args| Object.new }
+    s2 = OpenSSL::SSL::SSLSocket.new(sock2, ctx2)
+    assert_raise(ArgumentError) { s2.accept }
     assert t.join
   ensure
-    sock1.close if sock1
-    sock2.close if sock2
+    sock1.close
+    sock2.close
   end
 
   def test_accept_errors_include_peeraddr
@@ -1555,7 +1701,12 @@ def test_options_disable_versions
       # Client only supports TLS 1.3
       ctx2 = OpenSSL::SSL::SSLContext.new
       ctx2.min_version = ctx2.max_version = OpenSSL::SSL::TLS1_3_VERSION
-      assert_nothing_raised { server_connect(port, ctx2) { } }
+      assert_nothing_raised {
+        server_connect(port, ctx2) { |ssl|
+          # Ensure SSL_accept() finishes successfully
+          ssl.puts("abc"); ssl.gets
+        }
+      }
     }
 
     # Server only supports TLS 1.2