diff --git a/lib/index.js b/lib/index.js
index ce576dd88..7f1275d19 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -301,27 +301,27 @@ module.exports.render = function(options, cb) {
     if (Array.isArray(importer)) {
       importer.forEach(function(subject, index) {
         options.importer[index] = function(file, prev, bridge) {
-          function done(data) {
-            bridge.success(data);
+          function done(result) {
+            bridge.success(result === module.exports.NULL ? null : result);
           }
 
           var result = subject.call(options.context, file, prev, done);
 
-          if (result) {
-            done(result === module.exports.NULL ? null : result);
+          if (result !== undefined) {
+            done(result);
           }
         };
       });
     } else {
       options.importer = function(file, prev, bridge) {
-        function done(data) {
-          bridge.success(data);
+        function done(result) {
+          bridge.success(result === module.exports.NULL ? null : result);
         }
 
         var result = importer.call(options.context, file, prev, done);
 
-        if (result) {
-          done(result === module.exports.NULL ? null : result);
+        if (result !== undefined) {
+          done(result);
         }
       };
     }
diff --git a/src/custom_function_bridge.cpp b/src/custom_function_bridge.cpp
index f0e49b6c8..110b7d3d0 100644
--- a/src/custom_function_bridge.cpp
+++ b/src/custom_function_bridge.cpp
@@ -4,9 +4,13 @@
 #include "sass_types/factory.h"
 #include "sass_types/value.h"
 
+#include <stdio.h>
+
 Sass_Value* CustomFunctionBridge::post_process_return_value(v8::Local<v8::Value> val) const {
   SassTypes::Value *v_;
-  if ((v_ = SassTypes::Factory::unwrap(val))) {
+  if (val->IsNull()) {
+    return sass_make_null();
+  } else if ((v_ = SassTypes::Factory::unwrap(val))) {
     return v_->get_sass_value();
   } else {
     return sass_make_error("A SassValue object was expected.");
@@ -17,7 +21,15 @@ std::vector<v8::Local<v8::Value>> CustomFunctionBridge::pre_process_args(std::ve
   std::vector<v8::Local<v8::Value>> argv = std::vector<v8::Local<v8::Value>>();
 
   for (void* value : in) {
-    argv.push_back(SassTypes::Factory::create(static_cast<Sass_Value*>(value))->get_js_object());
+    Sass_Value *vptr = static_cast<Sass_Value*>(value);
+    v8::Local<v8::Value> item;
+
+    if (sass_value_is_null(vptr)) {
+        item = Nan::Null();
+    } else {
+        item = SassTypes::Factory::create(vptr)->get_js_object();
+    }
+    argv.push_back(item);
   }
 
   return argv;
diff --git a/src/sass_types/boolean.cpp b/src/sass_types/boolean.cpp
index 89c7a9659..61e2879c2 100644
--- a/src/sass_types/boolean.cpp
+++ b/src/sass_types/boolean.cpp
@@ -54,12 +54,12 @@ namespace SassTypes
 
     if (info.IsConstructCall()) {
       if (constructor_locked) {
-        return Nan::ThrowTypeError(Nan::New("Cannot instantiate SassBoolean").ToLocalChecked());
+        return Nan::ThrowTypeError("Cannot instantiate SassBoolean");
       }
     }
     else {
       if (info.Length() != 1 || !info[0]->IsBoolean()) {
-        return Nan::ThrowTypeError(Nan::New("Expected one boolean argument").ToLocalChecked());
+        return Nan::ThrowTypeError("Expected one boolean argument");
       }
 
       info.GetReturnValue().Set(get_singleton(Nan::To<bool>(info[0]).FromJust()).get_js_object());
diff --git a/src/sass_types/color.cpp b/src/sass_types/color.cpp
index ed22b13cb..f484b196e 100644
--- a/src/sass_types/color.cpp
+++ b/src/sass_types/color.cpp
@@ -79,11 +79,11 @@ namespace SassTypes
 
   NAN_METHOD(Color::SetR) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a number").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a number");
     }
 
     sass_color_set_r(unwrap(info.This())->value, Nan::To<double>(info[0]).FromJust());
@@ -91,11 +91,11 @@ namespace SassTypes
 
   NAN_METHOD(Color::SetG) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a number").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a number");
     }
 
     sass_color_set_g(unwrap(info.This())->value, Nan::To<double>(info[0]).FromJust());
@@ -103,11 +103,11 @@ namespace SassTypes
 
   NAN_METHOD(Color::SetB) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a number").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a number");
     }
 
     sass_color_set_b(unwrap(info.This())->value, Nan::To<double>(info[0]).FromJust());
@@ -115,11 +115,11 @@ namespace SassTypes
 
   NAN_METHOD(Color::SetA) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a number").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a number");
     }
 
     sass_color_set_a(unwrap(info.This())->value, Nan::To<double>(info[0]).FromJust());
diff --git a/src/sass_types/factory.cpp b/src/sass_types/factory.cpp
index 1c91f7a2f..a4aa1b924 100644
--- a/src/sass_types/factory.cpp
+++ b/src/sass_types/factory.cpp
@@ -40,13 +40,16 @@ namespace SassTypes
 
     default:
       const char *msg = "Unknown type encountered.";
-      Nan::ThrowTypeError(Nan::New<v8::String>(msg).ToLocalChecked());
+      Nan::ThrowTypeError(msg);
       return new Error(sass_make_error(msg));
     }
   }
 
   NAN_MODULE_INIT(Factory::initExports) {
     Nan::HandleScope scope;
+    v8::Local<v8::Object> fake_null = Nan::New<v8::Object>();
+    Nan::Set(fake_null, Nan::New("NULL").ToLocalChecked(), Nan::Null());
+
     v8::Local<v8::Object> types = Nan::New<v8::Object>();
 
     Nan::Set(types, Nan::New("Number").ToLocalChecked(), Number::get_constructor());
@@ -55,7 +58,7 @@ namespace SassTypes
     Nan::Set(types, Nan::New("Boolean").ToLocalChecked(), Boolean::get_constructor());
     Nan::Set(types, Nan::New("List").ToLocalChecked(), List::get_constructor());
     Nan::Set(types, Nan::New("Map").ToLocalChecked(), Map::get_constructor());
-    Nan::Set(types, Nan::New("Null").ToLocalChecked(), Null::get_constructor());
+    Nan::Set(types, Nan::New("Null").ToLocalChecked(), fake_null);
     Nan::Set(types, Nan::New("Error").ToLocalChecked(), Error::get_constructor());
     Nan::Set(target, Nan::New<v8::String>("types").ToLocalChecked(), types);
   }
diff --git a/src/sass_types/list.cpp b/src/sass_types/list.cpp
index a337d638e..0d68b2831 100644
--- a/src/sass_types/list.cpp
+++ b/src/sass_types/list.cpp
@@ -39,11 +39,11 @@ namespace SassTypes
   NAN_METHOD(List::GetValue) {
 
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied index should be an integer").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied index should be an integer");
     }
 
     Sass_Value* list = unwrap(info.This())->value;
@@ -54,27 +54,36 @@ namespace SassTypes
       return Nan::ThrowRangeError(Nan::New("Out of bound index").ToLocalChecked());
     }
 
-    info.GetReturnValue().Set(Factory::create(sass_list_get_value(list, Nan::To<uint32_t>(info[0]).FromJust()))->get_js_object());
+    Sass_Value *item = sass_list_get_value(list, Nan::To<uint32_t>(info[0]).FromJust());
+    if (sass_value_is_null(item)) {
+      info.GetReturnValue().Set(Nan::Null());
+    } else {
+      info.GetReturnValue().Set(Factory::create(item)->get_js_object());
+    }
   }
 
   NAN_METHOD(List::SetValue) {
     if (info.Length() != 2) {
-      return Nan::ThrowTypeError(Nan::New("Expected two arguments").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected two arguments");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied index should be an integer").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied index should be an integer");
     }
 
+    if (info[1]->IsNull()) {
+      sass_list_set_value(unwrap(info.This())->value, Nan::To<uint32_t>(info[0]).FromJust(), sass_make_null());
+      return;
+    }
     if (!info[1]->IsObject()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a SassValue object").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a SassValue object");
     }
 
     Value* sass_value = Factory::unwrap(info[1]);
     if (sass_value) {
       sass_list_set_value(unwrap(info.This())->value, Nan::To<uint32_t>(info[0]).FromJust(), sass_value->get_sass_value());
     } else {
-      Nan::ThrowTypeError(Nan::New<v8::String>("A SassValue is expected as the list item").ToLocalChecked());
+      Nan::ThrowTypeError("A SassValue is expected as the list item");
     }
   }
 
@@ -84,11 +93,11 @@ namespace SassTypes
 
   NAN_METHOD(List::SetSeparator) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsBoolean()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a boolean").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a boolean");
     }
 
     sass_list_set_separator(unwrap(info.This())->value, Nan::To<bool>(info[0]).FromJust() ? SASS_COMMA : SASS_SPACE);
diff --git a/src/sass_types/map.cpp b/src/sass_types/map.cpp
index 147de42f4..ad147e6f9 100644
--- a/src/sass_types/map.cpp
+++ b/src/sass_types/map.cpp
@@ -30,11 +30,11 @@ namespace SassTypes
   NAN_METHOD(Map::GetValue) {
 
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied index should be an integer").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied index should be an integer");
     }
 
     Sass_Value* map = unwrap(info.This())->value;
@@ -50,33 +50,33 @@ namespace SassTypes
 
   NAN_METHOD(Map::SetValue) {
     if (info.Length() != 2) {
-      return Nan::ThrowTypeError(Nan::New("Expected two arguments").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected two arguments");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied index should be an integer").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied index should be an integer");
     }
 
     if (!info[1]->IsObject()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a SassValue object").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a SassValue object");
     }
 
     Value* sass_value = Factory::unwrap(info[1]);
     if (sass_value) {
       sass_map_set_value(unwrap(info.This())->value, Nan::To<uint32_t>(info[0]).FromJust(), sass_value->get_sass_value());
     } else {
-      Nan::ThrowTypeError(Nan::New<v8::String>("A SassValue is expected as a map value").ToLocalChecked());
+      Nan::ThrowTypeError("A SassValue is expected as a map value");
     }
   }
 
   NAN_METHOD(Map::GetKey) {
 
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied index should be an integer").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied index should be an integer");
     }
 
     Sass_Value* map = unwrap(info.This())->value;
@@ -92,22 +92,22 @@ namespace SassTypes
 
   NAN_METHOD(Map::SetKey) {
     if (info.Length() != 2) {
-      return Nan::ThrowTypeError(Nan::New("Expected two arguments").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected two arguments");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied index should be an integer").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied index should be an integer");
     }
 
     if (!info[1]->IsObject()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a SassValue object").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a SassValue object");
     }
 
     Value* sass_value = Factory::unwrap(info[1]);
     if (sass_value) {
       sass_map_set_key(unwrap(info.This())->value, Nan::To<uint32_t>(info[0]).FromJust(), sass_value->get_sass_value());
     } else {
-      Nan::ThrowTypeError(Nan::New<v8::String>("A SassValue is expected as a map key").ToLocalChecked());
+      Nan::ThrowTypeError("A SassValue is expected as a map key");
     }
   }
 
diff --git a/src/sass_types/null.cpp b/src/sass_types/null.cpp
index 4e3536d6c..766cdf935 100644
--- a/src/sass_types/null.cpp
+++ b/src/sass_types/null.cpp
@@ -49,7 +49,7 @@ namespace SassTypes
 
     if (info.IsConstructCall()) {
       if (constructor_locked) {
-        return Nan::ThrowTypeError(Nan::New("Cannot instantiate SassNull").ToLocalChecked());
+        return Nan::ThrowTypeError("Cannot instantiate SassNull");
       }
     }
     else {
diff --git a/src/sass_types/number.cpp b/src/sass_types/number.cpp
index 1605516b2..e98d1e302 100644
--- a/src/sass_types/number.cpp
+++ b/src/sass_types/number.cpp
@@ -47,11 +47,11 @@ namespace SassTypes
   NAN_METHOD(Number::SetValue) {
 
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsNumber()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a number").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a number");
     }
 
     sass_number_set_value(unwrap(info.This())->value, Nan::To<double>(info[0]).FromJust());
@@ -59,11 +59,11 @@ namespace SassTypes
 
   NAN_METHOD(Number::SetUnit) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsString()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a string").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a string");
     }
 
     sass_number_set_unit(unwrap(info.This())->value, create_string(info[0]));
diff --git a/src/sass_types/string.cpp b/src/sass_types/string.cpp
index d97095bbc..c72a93a95 100644
--- a/src/sass_types/string.cpp
+++ b/src/sass_types/string.cpp
@@ -31,11 +31,11 @@ namespace SassTypes
 
   NAN_METHOD(String::SetValue) {
     if (info.Length() != 1) {
-      return Nan::ThrowTypeError(Nan::New("Expected just one argument").ToLocalChecked());
+      return Nan::ThrowTypeError("Expected just one argument");
     }
 
     if (!info[0]->IsString()) {
-      return Nan::ThrowTypeError(Nan::New("Supplied value should be a string").ToLocalChecked());
+      return Nan::ThrowTypeError("Supplied value should be a string");
     }
 
     sass_string_set_value(unwrap(info.This())->value, create_string(info[0]));
diff --git a/test/api.js b/test/api.js
index f289272c1..a9f7d8e6a 100644
--- a/test/api.js
+++ b/test/api.js
@@ -956,50 +956,49 @@ describe('api', function() {
         data: 'div { color: foo(bar(null)); background-color: baz("foo" == "bar"); }',
         functions: {
           foo: function(a) {
-            assert.ok(
-              'Supplied value should be the same instance as sass.TRUE',
-              a === sass.TRUE
+            assert.strictEqual(a, sass.TRUE,
+              'Supplied value should be the same instance as sass.TRUE'
             );
 
-            assert.ok(
-              'sass.types.Boolean(true) should return a singleton',
-              sass.types.Boolean(true) === sass.types.Boolean(true) &&
-              sass.types.Boolean(true) === sass.TRUE
-            );
+            assert.strictEqual(
+              sass.types.Boolean(true), sass.types.Boolean(true),
+              'sass.types.Boolean(true) should return a singleton');
+
+            assert.strictEqual(
+              sass.types.Boolean(true), sass.TRUE,
+              'sass.types.Boolean(true) should be the same instance as sass.TRUE');
 
             counter++;
 
             return sass.types.String('foo');
           },
           bar: function(a) {
-            assert.ok(
-              'Supplied value should be the same instance as sass.NULL',
-              a === sass.NULL
-            );
+            assert.strictEqual(a, sass.NULL, 
+                'Supplied value should be the same instance as sass.NULL');
 
             assert.throws(function() {
               return new sass.types.Null();
-            }, /Cannot instantiate SassNull/);
+            });
 
             counter++;
 
             return sass.TRUE;
           },
           baz: function(a) {
-            assert.ok(
-              'Supplied value should be the same instance as sass.FALSE',
-              a === sass.FALSE
-            );
+            assert.strictEqual(a, sass.FALSE,
+              'Supplied value should be the same instance as sass.FALSE');
 
             assert.throws(function() {
               return new sass.types.Boolean(false);
             }, /Cannot instantiate SassBoolean/);
 
-            assert.ok(
-              'sass.types.Boolean(false) should return a singleton',
-              sass.types.Boolean(false) === sass.types.Boolean(false) &&
-              sass.types.Boolean(false) === sass.FALSE
-            );
+            assert.strictEqual(
+              sass.types.Boolean(false), sass.types.Boolean(false),
+              'sass.types.Boolean(false) should return a singleton');
+
+            assert.strictEqual(
+              sass.types.Boolean(false), sass.FALSE,
+              'sass.types.Boolean(false) should return singleton identical to sass.FALSE');
 
             counter++;
 
@@ -1007,7 +1006,7 @@ describe('api', function() {
           }
         }
       }, function() {
-        assert.ok(counter === 3);
+        assert.strictEqual(counter, 3);
         done();
       });
     });
@@ -1021,7 +1020,7 @@ describe('api', function() {
         file: fixture('include-files/index.scss')
       }, function(error, result) {
         assert(!error);
-        assert(typeof result.stats.start === 'number');
+        assert.strictEqual(typeof result.stats.start, 'number');
         assert(result.stats.start >= start);
         done();
       });
@@ -1032,7 +1031,7 @@ describe('api', function() {
         file: fixture('include-files/index.scss')
       }, function(error, result) {
         assert(!error);
-        assert(typeof result.stats.end === 'number');
+        assert.strictEqual(typeof result.stats.end, 'number');
         assert(result.stats.end >= result.stats.start);
         done();
       });
@@ -1043,7 +1042,7 @@ describe('api', function() {
         file: fixture('include-files/index.scss')
       }, function(error, result) {
         assert(!error);
-        assert(typeof result.stats.duration === 'number');
+        assert.strictEqual(typeof result.stats.duration, 'number');
         assert.equal(result.stats.end - result.stats.start, result.stats.duration);
         done();
       });
@@ -1504,19 +1503,19 @@ describe('api', function() {
     });
 
     it('should provide a start timestamp', function(done) {
-      assert(typeof result.stats.start === 'number');
+      assert.strictEqual(typeof result.stats.start, 'number');
       assert(result.stats.start >= start);
       done();
     });
 
     it('should provide an end timestamp', function(done) {
-      assert(typeof result.stats.end === 'number');
+      assert.strictEqual(typeof result.stats.end, 'number');
       assert(result.stats.end >= result.stats.start);
       done();
     });
 
     it('should provide a duration', function(done) {
-      assert(typeof result.stats.duration === 'number');
+      assert.strictEqual(typeof result.stats.duration, 'number');
       assert.equal(result.stats.end - result.stats.start, result.stats.duration);
       done();
     });
diff --git a/test/cli.js b/test/cli.js
index ba48fb864..b377bd602 100644
--- a/test/cli.js
+++ b/test/cli.js
@@ -244,7 +244,7 @@ describe('cli', function() {
 
       bin.stderr.setEncoding('utf8');
       bin.stderr.once('data', function(data) {
-        assert(data.trim() === '=> changed: ' + src);
+        assert.strictEqual(data.trim(), '=> changed: ' + src);
         fs.unlinkSync(src);
         bin.kill();
         done();
@@ -290,7 +290,7 @@ describe('cli', function() {
 
       bin.stdout.setEncoding('utf8');
       bin.stdout.once('data', function(data) {
-        assert(data.trim() === 'body{background:white}');
+        assert.strictEqual(data.trim(), 'body{background:white}');
         fs.unlinkSync(src);
         bin.kill();
         done();
@@ -314,7 +314,7 @@ describe('cli', function() {
 
       bin.stdout.setEncoding('utf8');
       bin.stdout.once('data', function(data) {
-        assert.equal(data.trim(), 'body{background:blue}');
+        assert.strictEqual(data.trim(), 'body{background:blue}');
         bin.kill();
         done();
       });
@@ -337,7 +337,7 @@ describe('cli', function() {
 
       bin.stdout.setEncoding('utf8');
       bin.stdout.once('data', function(data) {
-        assert.equal(data.trim(), 'body{background:red}');
+        assert.strictEqual(data.trim(), 'body{background:red}');
         bin.kill();
         done();
       });
@@ -442,7 +442,7 @@ describe('cli', function() {
       ]);
 
       bin.once('close', function() {
-        assert(read(dest, 'utf8').indexOf('sourceMappingURL') === -1);
+        assert.strictEqual(read(dest, 'utf8').indexOf('sourceMappingURL'), -1);
         assert(fs.existsSync(map));
         fs.unlinkSync(map);
         fs.unlinkSync(dest);
@@ -570,8 +570,8 @@ describe('cli', function() {
       var bin = spawn(cli, [src]);
 
       bin.once('close', function(code) {
-        assert(code !== 0);
-        assert.equal(glob.sync(fixture('input-directory/**/*.css')).length, 0);
+        assert.notStrictEqual(code, 0);
+        assert.strictEqual(glob.sync(fixture('input-directory/**/*.css')).length, 0);
         done();
       });
     });
@@ -582,7 +582,7 @@ describe('cli', function() {
       var bin = spawn(cli, [src, '--output', dest]);
 
       bin.once('close', function(code) {
-        assert(code !== 0);
+        assert.notStrictEqual(code, 0);
         assert.equal(glob.sync(fixture('input-directory/**/*.css')).length, 0);
         done();
       });
@@ -745,7 +745,7 @@ describe('cli', function() {
       ]);
 
       bin.once('close', function(code) {
-        assert(code !== 0);
+        assert.notStrictEqual(code, 0);
         done();
       });
     });