diff --git a/composer.json b/composer.json
index ab63538..676c53f 100644
--- a/composer.json
+++ b/composer.json
@@ -21,7 +21,8 @@
     },
     "require": {
         "php": ">=5.5",
-        "symfony/http-foundation": "~2.8|~3.0"
+        "symfony/http-foundation": "~2.8|~3.0",
+        "psr/http-message": "^1.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.8",
diff --git a/src/Signature.php b/src/Signature.php
index f21c7c3..d3f34fd 100644
--- a/src/Signature.php
+++ b/src/Signature.php
@@ -2,49 +2,37 @@
 
 namespace HttpSignatures;
 
-use Symfony\Component\HttpFoundation\Request;
+use Psr\Http\Message\MessageInterface;
 
 class Signature
 {
-    /** @var Request|SymfonyRequestMessage */
-    private $message;
-
     /** @var Key */
     private $key;
 
     /** @var HmacAlgorithm */
     private $algorithm;
 
-    /** @var HeaderList */
-    private $headerList;
+    /** @var SigningString */
+    private $signingString;
 
     /**
-     * @param Request|SymfonyRequestMessage $message
-     * @param Key                           $key
-     * @param HmacAlgorithm                 $algorithm
-     * @param HeaderList                    $headerList
+     * @param MessageInterface $message
+     * @param Key $key
+     * @param HmacAlgorithm $algorithm
+     * @param HeaderList $headerList
      */
     public function __construct($message, $key, $algorithm, $headerList)
     {
-        $this->message = $message;
         $this->key = $key;
         $this->algorithm = $algorithm;
-        $this->headerList = $headerList;
+        $this->signingString = new SigningString($headerList, $message);
     }
 
     public function string()
     {
         return $this->algorithm->sign(
             $this->key->secret,
-            $this->signingString()->string()
-        );
-    }
-
-    private function signingString()
-    {
-        return new SigningString(
-            $this->headerList,
-            $this->message
+            $this->signingString->string()
         );
     }
 }
diff --git a/src/Signer.php b/src/Signer.php
index f85c8dc..a436d4d 100644
--- a/src/Signer.php
+++ b/src/Signer.php
@@ -43,11 +43,11 @@ public function sign($message)
     private function signatureParameters($message)
     {
         return new SignatureParameters(
-        $this->key,
-        $this->algorithm,
-        $this->headerList,
-        $this->signature($message)
-      );
+            $this->key,
+            $this->algorithm,
+            $this->headerList,
+            $this->signature($message)
+        );
     }
 
     /**
diff --git a/src/SigningString.php b/src/SigningString.php
index 2a21917..c13fcf1 100644
--- a/src/SigningString.php
+++ b/src/SigningString.php
@@ -2,28 +2,25 @@
 
 namespace HttpSignatures;
 
-use Symfony\Component\HttpFoundation\Request;
+use Psr\Http\Message\MessageInterface;
+use Psr\Http\Message\RequestInterface;
 
 class SigningString
 {
     /** @var HeaderList */
     private $headerList;
 
-    /** @var Request|SymfonyRequestMessage */
+    /** @var RequestInterface */
     private $message;
 
     /**
-     * @param HeaderList                    $headerList
-     * @param Request|SymfonyRequestMessage $message
+     * @param HeaderList $headerList
+     * @param MessageInterface $message
      */
     public function __construct($headerList, $message)
     {
         $this->headerList = $headerList;
-        if ($message instanceof Request) {
-            $this->message = new SymfonyRequestMessage($message);
-        } else {
-            $this->message = $message;
-        }
+        $this->message = $message;
     }
 
     /**
@@ -70,9 +67,8 @@ private function line($name)
      */
     private function headerValue($name)
     {
-        $headers = $this->message->headers;
-        if ($headers->has($name)) {
-            return $headers->get($name);
+        if ($this->message->hasHeader($name)) {
+            return $this->message->getHeader($name);
         } else {
             throw new SignedHeaderNotPresentException("Header '$name' not in message");
         }
@@ -95,8 +91,8 @@ private function requestTargetLine()
      */
     private function getPathWithQueryString()
     {
-        $path = $this->message->getPathInfo();
-        $qs = $this->message->getQueryString();
+        $path = $this->message->getUri()->getPath();
+        $qs = $this->message->getUri()->getQuery();
         if ($qs === null) {
             return $path;
         } else {
diff --git a/src/Verification.php b/src/Verification.php
index e08efb9..b0bd8ff 100644
--- a/src/Verification.php
+++ b/src/Verification.php
@@ -2,11 +2,11 @@
 
 namespace HttpSignatures;
 
-use Symfony\Component\HttpFoundation\Request;
+use Psr\Http\Message\MessageInterface;
 
 class Verification
 {
-    /** @var Request|SymfonyRequestMessage */
+    /** @var MessageInterface */
     private $message;
 
     /** @var KeyStoreInterface */
@@ -16,10 +16,10 @@ class Verification
     private $_parameters;
 
     /**
-     * @param Request|SymfonyRequestMessage $message
-     * @param KeyStoreInterface             $keyStore
+     * @param MessageInterface $message
+     * @param KeyStoreInterface $keyStore
      */
-    public function __construct($message, KeyStoreInterface $keyStore)
+    public function __construct($message, $keyStore)
     {
         $this->message = $message;
         $this->keyStore = $keyStore;
@@ -147,7 +147,7 @@ private function parameters()
      */
     private function hasSignatureHeader()
     {
-        return $this->message->headers->has('Signature') || $this->message->headers->has('Authorization');
+        return $this->message->hasHeader('Signature') || $this->message->hasHeader('Authorization');
     }
 
     /**
@@ -173,8 +173,6 @@ private function signatureHeader()
      */
     private function fetchHeader($name)
     {
-        $headers = $this->message->headers;
-
-        return $headers->has($name) ? $headers->get($name) : null;
+        return $this->message->getHeader($name);
     }
 }
diff --git a/src/Verifier.php b/src/Verifier.php
index bcdd678..a764d01 100644
--- a/src/Verifier.php
+++ b/src/Verifier.php
@@ -2,7 +2,7 @@
 
 namespace HttpSignatures;
 
-use Symfony\Component\HttpFoundation\Request;
+use Psr\Http\Message\MessageInterface;
 
 class Verifier
 {
@@ -18,8 +18,7 @@ public function __construct(KeyStoreInterface $keyStore)
     }
 
     /**
-     * @param Request|SymfonyRequestMessage $message
-     *
+     * @param MessageInterface $message
      * @return bool
      */
     public function isValid($message)