diff --git a/src/json/JsonReference.php b/src/json/JsonReference.php
index fe27ced..cfac559 100644
--- a/src/json/JsonReference.php
+++ b/src/json/JsonReference.php
@@ -126,6 +126,7 @@ public function getReference(): string
      * @return mixed data which can be serialized by <b>json_encode</b>,
      * which is a value of any type other than a resource.
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return (object)['$ref' => $this->getReference()];
diff --git a/src/spec/OpenApi.php b/src/spec/OpenApi.php
index 7476ce8..4010093 100644
--- a/src/spec/OpenApi.php
+++ b/src/spec/OpenApi.php
@@ -107,7 +107,7 @@ public function performValidation()
      */
     public function getMajorVersion()
     {
-        if (preg_match(static::PATTERN_VERSION, $this->openapi, $matches)) {
+        if (is_string($this->openapi) && preg_match(static::PATTERN_VERSION, $this->openapi, $matches)) {
             switch ($matches[1]) {
                 case '3.0':
                     return static::VERSION_3_0;
diff --git a/src/spec/Paths.php b/src/spec/Paths.php
index a2da8a1..6bb8625 100644
--- a/src/spec/Paths.php
+++ b/src/spec/Paths.php
@@ -183,7 +183,7 @@ public function getErrors(): array
      * @return boolean true on success or false on failure.
      * The return value will be casted to boolean if non-boolean was returned.
      */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return $this->hasPath($offset);
     }
@@ -194,6 +194,7 @@ public function offsetExists($offset)
      * @param mixed $offset The offset to retrieve.
      * @return PathItem Can return all value types.
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->getPath($offset);
@@ -205,7 +206,7 @@ public function offsetGet($offset)
      * @param mixed $offset The offset to assign the value to.
      * @param mixed $value The value to set.
      */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->addPath($offset, $value);
     }
@@ -215,7 +216,7 @@ public function offsetSet($offset, $value)
      * @link http://php.net/manual/en/arrayaccess.offsetunset.php
      * @param mixed $offset The offset to unset.
      */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         $this->removePath($offset);
     }
@@ -226,7 +227,7 @@ public function offsetUnset($offset)
      * @return int The custom count as an integer.
      * The return value is cast to an integer.
      */
-    public function count()
+    public function count(): int
     {
         return count($this->_paths);
     }
@@ -236,7 +237,7 @@ public function count()
      * @link http://php.net/manual/en/iteratoraggregate.getiterator.php
      * @return Traversable An instance of an object implementing <b>Iterator</b> or <b>Traversable</b>
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->_paths);
     }
diff --git a/src/spec/Responses.php b/src/spec/Responses.php
index a3623ae..82ecbb7 100644
--- a/src/spec/Responses.php
+++ b/src/spec/Responses.php
@@ -173,7 +173,7 @@ public function getErrors(): array
      * @return boolean true on success or false on failure.
      * The return value will be casted to boolean if non-boolean was returned.
      */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return $this->hasResponse($offset);
     }
@@ -184,6 +184,7 @@ public function offsetExists($offset)
      * @param mixed $offset The offset to retrieve.
      * @return mixed Can return all value types.
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->getResponse($offset);
@@ -195,7 +196,7 @@ public function offsetGet($offset)
      * @param mixed $offset The offset to assign the value to.
      * @param mixed $value The value to set.
      */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         $this->addResponse($offset, $value);
     }
@@ -205,7 +206,7 @@ public function offsetSet($offset, $value)
      * @link http://php.net/manual/en/arrayaccess.offsetunset.php
      * @param mixed $offset The offset to unset.
      */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         $this->removeResponse($offset);
     }
@@ -216,7 +217,7 @@ public function offsetUnset($offset)
      * @return int The custom count as an integer.
      * The return value is cast to an integer.
      */
-    public function count()
+    public function count(): int
     {
         return count($this->_responses);
     }
@@ -226,7 +227,7 @@ public function count()
      * @link http://php.net/manual/en/iteratoraggregate.getiterator.php
      * @return Traversable An instance of an object implementing <b>Iterator</b> or <b>Traversable</b>
      */
-    public function getIterator()
+    public function getIterator(): Traversable
     {
         return new ArrayIterator($this->_responses);
     }