diff --git a/plugins/OStatus/lib/magicenvelope.php b/plugins/OStatus/lib/magicenvelope.php
index 6d3956cb9b..384506280d 100644
--- a/plugins/OStatus/lib/magicenvelope.php
+++ b/plugins/OStatus/lib/magicenvelope.php
@@ -80,6 +80,20 @@ class MagicEnvelope
         throw new Exception(_m('Unable to locate signer public key.'));
     }
 
+    /**
+     * The current MagicEnvelope spec as used in StatusNet 0.9.7 and later
+     * includes both the original data and some signing metadata fields as
+     * the input plaintext for the signature hash.
+     *
+     * @param array $env
+     * @return string
+     */
+    public function signingText($env) {
+        return implode('.', array($env['data'], // this field is pre-base64'd
+                            Magicsig::base64_url_encode($env['data_type']),
+                            Magicsig::base64_url_encode($env['encoding']),
+                            Magicsig::base64_url_encode($env['alg'])));
+    }
 
     /**
      *
@@ -93,14 +107,17 @@ class MagicEnvelope
     {
         $signature_alg = Magicsig::fromString($keypair);
         $armored_text = Magicsig::base64_url_encode($text);
-
-        return array(
+        $env = array(
             'data' => $armored_text,
             'encoding' => MagicEnvelope::ENCODING,
             'data_type' => $mimetype,
-            'sig' => $signature_alg->sign($armored_text),
+            'sig' => '',
             'alg' => $signature_alg->getName()
         );
+
+        $env['sig'] = $signature_alg->sign($this->signingText($env));
+
+        return $env;
     }
 
     /**
@@ -239,7 +256,7 @@ class MagicEnvelope
             return false;
         }
 
-        return $verifier->verify($env['data'], $env['sig']);
+        return $verifier->verify($this->signingText($env), $env['sig']);
     }
 
     /**
@@ -290,3 +307,24 @@ class MagicEnvelope
         );
     }
 }
+
+/**
+ * Variant of MagicEnvelope using the earlier signature form listed in the MagicEnvelope
+ * spec in early 2010; this was used in StatusNet up through 0.9.6, so for backwards compatiblity
+ * we still need to accept and sometimes send this format.
+ */
+class MagicEnvelopeCompat extends MagicEnvelope {
+
+    /**
+     * StatusNet through 0.9.6 used an earlier version of the MagicEnvelope spec
+     * which used only the input data, without the additional fields, as the plaintext
+     * for signing.
+     *
+     * @param array $env
+     * @return string
+     */
+    public function signingText($env) {
+        return $env['data'];
+    }
+}
+
diff --git a/plugins/OStatus/tests/MagicEnvelopeTest.php b/plugins/OStatus/tests/MagicEnvelopeTest.php
new file mode 100644
index 0000000000..5ee0362d28
--- /dev/null
+++ b/plugins/OStatus/tests/MagicEnvelopeTest.php
@@ -0,0 +1,60 @@
+<?php
+
+if (isset($_SERVER) && array_key_exists('REQUEST_METHOD', $_SERVER)) {
+    print "This script must be run from the command line\n";
+    exit();
+}
+
+define('INSTALLDIR', realpath(dirname(__FILE__) . '/../../..'));
+define('STATUSNET', true);
+
+require_once INSTALLDIR . '/lib/common.php';
+
+class MagicEnvelopeTest extends PHPUnit_Framework_TestCase
+{
+    /**
+     * Test that MagicEnvelope builds the correct plaintext for signing.
+     * @dataProvider provider
+     */
+    public function testSignatureText($env, $expected)
+    {
+        $magic = new MagicEnvelope;
+        $text = $magic->signingText($env);
+
+        $this->assertEquals($expected, $text, "'$text' should be '$expected'");
+    }
+
+    static public function provider()
+    {
+        return array(
+            array(
+                // Sample case given in spec:
+                // http://salmon-protocol.googlecode.com/svn/trunk/draft-panzer-magicsig-00.html#signing
+                array(
+                    'data' => 'Tm90IHJlYWxseSBBdG9t',
+                    'data_type' => 'application/atom+xml',
+                    'encoding' => 'base64url',
+                    'alg' => 'RSA-SHA256'
+                ),
+                'Tm90IHJlYWxseSBBdG9t.YXBwbGljYXRpb24vYXRvbSt4bWw=.YmFzZTY0dXJs.UlNBLVNIQTI1Ng=='
+            )
+        );
+    }
+
+
+    /**
+     * Test that MagicEnvelope builds the correct plaintext for signing.
+     * @dataProvider provider
+     */
+    public function testSignatureTextCompat($env, $expected)
+    {
+        // Our old code didn't add the extra fields, just used the armored text.
+        $alt = $env['data'];
+
+        $magic = new MagicEnvelopeCompat;
+        $text = $magic->signingText($env);
+
+        $this->assertEquals($alt, $text, "'$text' should be '$alt'");
+    }
+
+}