diff --git a/composer.json b/composer.json
index b0d2937..56e8c0a 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0"
+        "php": "^7.2 || ^8.0"
     },
     "autoload": {
         "psr-4": {
@@ -20,7 +20,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "1.0.x-dev"
+            "dev-master": "1.1.x-dev"
         }
     }
 }
diff --git a/src/MessageInterface.php b/src/MessageInterface.php
index dd46e5e..8cdb4ed 100644
--- a/src/MessageInterface.php
+++ b/src/MessageInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -38,7 +40,7 @@ public function getProtocolVersion();
      * @param string $version HTTP protocol version
      * @return static
      */
-    public function withProtocolVersion($version);
+    public function withProtocolVersion(string $version);
 
     /**
      * Retrieves all message header values.
@@ -75,7 +77,7 @@ public function getHeaders();
      *     name using a case-insensitive string comparison. Returns false if
      *     no matching header name is found in the message.
      */
-    public function hasHeader($name);
+    public function hasHeader(string $name);
 
     /**
      * Retrieves a message header value by the given case-insensitive name.
@@ -91,7 +93,7 @@ public function hasHeader($name);
      *    header. If the header does not appear in the message, this method MUST
      *    return an empty array.
      */
-    public function getHeader($name);
+    public function getHeader(string $name);
 
     /**
      * Retrieves a comma-separated string of the values for a single header.
@@ -112,7 +114,7 @@ public function getHeader($name);
      *    concatenated together using a comma. If the header does not appear in
      *    the message, this method MUST return an empty string.
      */
-    public function getHeaderLine($name);
+    public function getHeaderLine(string $name);
 
     /**
      * Return an instance with the provided value replacing the specified header.
@@ -129,7 +131,7 @@ public function getHeaderLine($name);
      * @return static
      * @throws \InvalidArgumentException for invalid header names or values.
      */
-    public function withHeader($name, $value);
+    public function withHeader(string $name, $value);
 
     /**
      * Return an instance with the specified header appended with the given value.
@@ -147,7 +149,7 @@ public function withHeader($name, $value);
      * @return static
      * @throws \InvalidArgumentException for invalid header names or values.
      */
-    public function withAddedHeader($name, $value);
+    public function withAddedHeader(string $name, $value);
 
     /**
      * Return an instance without the specified header.
@@ -161,7 +163,7 @@ public function withAddedHeader($name, $value);
      * @param string $name Case-insensitive header field name to remove.
      * @return static
      */
-    public function withoutHeader($name);
+    public function withoutHeader(string $name);
 
     /**
      * Gets the body of the message.
diff --git a/src/RequestInterface.php b/src/RequestInterface.php
index a96d4fd..38066df 100644
--- a/src/RequestInterface.php
+++ b/src/RequestInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -55,10 +57,10 @@ public function getRequestTarget();
      *
      * @link http://tools.ietf.org/html/rfc7230#section-5.3 (for the various
      *     request-target forms allowed in request messages)
-     * @param mixed $requestTarget
+     * @param string $requestTarget
      * @return static
      */
-    public function withRequestTarget($requestTarget);
+    public function withRequestTarget(string $requestTarget);
 
     /**
      * Retrieves the HTTP method of the request.
@@ -82,7 +84,7 @@ public function getMethod();
      * @return static
      * @throws \InvalidArgumentException for invalid HTTP methods.
      */
-    public function withMethod($method);
+    public function withMethod(string $method);
 
     /**
      * Retrieves the URI instance.
@@ -125,5 +127,5 @@ public function getUri();
      * @param bool $preserveHost Preserve the original state of the Host header.
      * @return static
      */
-    public function withUri(UriInterface $uri, $preserveHost = false);
+    public function withUri(UriInterface $uri, bool $preserveHost = false);
 }
diff --git a/src/ResponseInterface.php b/src/ResponseInterface.php
index c306514..f85ca48 100644
--- a/src/ResponseInterface.php
+++ b/src/ResponseInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -49,7 +51,7 @@ public function getStatusCode();
      * @return static
      * @throws \InvalidArgumentException For invalid status code arguments.
      */
-    public function withStatus($code, $reasonPhrase = '');
+    public function withStatus(int $code, string $reasonPhrase = '');
 
     /**
      * Gets the response reason phrase associated with the status code.
diff --git a/src/ServerRequestInterface.php b/src/ServerRequestInterface.php
index 0251234..5e6d964 100644
--- a/src/ServerRequestInterface.php
+++ b/src/ServerRequestInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -224,7 +226,7 @@ public function getAttributes();
      * @param mixed $default Default value to return if the attribute does not exist.
      * @return mixed
      */
-    public function getAttribute($name, $default = null);
+    public function getAttribute(string $name, $default = null);
 
     /**
      * Return an instance with the specified derived request attribute.
@@ -241,7 +243,7 @@ public function getAttribute($name, $default = null);
      * @param mixed $value The value of the attribute.
      * @return static
      */
-    public function withAttribute($name, $value);
+    public function withAttribute(string $name, $value);
 
     /**
      * Return an instance that removes the specified derived request attribute.
@@ -257,5 +259,5 @@ public function withAttribute($name, $value);
      * @param string $name The attribute name.
      * @return static
      */
-    public function withoutAttribute($name);
+    public function withoutAttribute(string $name);
 }
diff --git a/src/StreamInterface.php b/src/StreamInterface.php
index f68f391..5924663 100644
--- a/src/StreamInterface.php
+++ b/src/StreamInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -84,7 +86,7 @@ public function isSeekable();
      *     SEEK_END: Set position to end-of-stream plus offset.
      * @throws \RuntimeException on failure.
      */
-    public function seek($offset, $whence = SEEK_SET);
+    public function seek(int $offset, int $whence = SEEK_SET);
 
     /**
      * Seek to the beginning of the stream.
@@ -112,7 +114,7 @@ public function isWritable();
      * @return int Returns the number of bytes written to the stream.
      * @throws \RuntimeException on failure.
      */
-    public function write($string);
+    public function write(string $string);
 
     /**
      * Returns whether or not the stream is readable.
@@ -131,7 +133,7 @@ public function isReadable();
      *     if no bytes are available.
      * @throws \RuntimeException if an error occurs.
      */
-    public function read($length);
+    public function read(int $length);
 
     /**
      * Returns the remaining contents in a string
@@ -149,10 +151,10 @@ public function getContents();
      * stream_get_meta_data() function.
      *
      * @link http://php.net/manual/en/function.stream-get-meta-data.php
-     * @param string $key Specific metadata to retrieve.
+     * @param string|null $key Specific metadata to retrieve.
      * @return array|mixed|null Returns an associative array if no key is
      *     provided. Returns a specific key value if a key is provided and the
      *     value is found, or null if the key is not found.
      */
-    public function getMetadata($key = null);
+    public function getMetadata(?string $key = null);
 }
diff --git a/src/UploadedFileInterface.php b/src/UploadedFileInterface.php
index f8a6901..aba6321 100644
--- a/src/UploadedFileInterface.php
+++ b/src/UploadedFileInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -62,7 +64,7 @@ public function getStream();
      * @throws \RuntimeException on any error during the move operation, or on
      *     the second or subsequent call to the method.
      */
-    public function moveTo($targetPath);
+    public function moveTo(string $targetPath);
     
     /**
      * Retrieve the file size.
diff --git a/src/UriInterface.php b/src/UriInterface.php
index 9d7ab9e..d974de0 100644
--- a/src/UriInterface.php
+++ b/src/UriInterface.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 namespace Psr\Http\Message;
 
 /**
@@ -188,7 +191,7 @@ public function getFragment();
      * @return static A new instance with the specified scheme.
      * @throws \InvalidArgumentException for invalid or unsupported schemes.
      */
-    public function withScheme($scheme);
+    public function withScheme(string $scheme);
 
     /**
      * Return an instance with the specified user information.
@@ -204,7 +207,7 @@ public function withScheme($scheme);
      * @param null|string $password The password associated with $user.
      * @return static A new instance with the specified user information.
      */
-    public function withUserInfo($user, $password = null);
+    public function withUserInfo(string $user, ?string $password = null);
 
     /**
      * Return an instance with the specified host.
@@ -218,7 +221,7 @@ public function withUserInfo($user, $password = null);
      * @return static A new instance with the specified host.
      * @throws \InvalidArgumentException for invalid hostnames.
      */
-    public function withHost($host);
+    public function withHost(string $host);
 
     /**
      * Return an instance with the specified port.
@@ -237,7 +240,7 @@ public function withHost($host);
      * @return static A new instance with the specified port.
      * @throws \InvalidArgumentException for invalid ports.
      */
-    public function withPort($port);
+    public function withPort(?int $port);
 
     /**
      * Return an instance with the specified path.
@@ -261,7 +264,7 @@ public function withPort($port);
      * @return static A new instance with the specified path.
      * @throws \InvalidArgumentException for invalid paths.
      */
-    public function withPath($path);
+    public function withPath(string $path);
 
     /**
      * Return an instance with the specified query string.
@@ -278,7 +281,7 @@ public function withPath($path);
      * @return static A new instance with the specified query string.
      * @throws \InvalidArgumentException for invalid query strings.
      */
-    public function withQuery($query);
+    public function withQuery(string $query);
 
     /**
      * Return an instance with the specified URI fragment.
@@ -294,7 +297,7 @@ public function withQuery($query);
      * @param string $fragment The fragment to use with the new instance.
      * @return static A new instance with the specified fragment.
      */
-    public function withFragment($fragment);
+    public function withFragment(string $fragment);
 
     /**
      * Return the string representation as a URI reference.