diff --git a/library/Zend/Http/UserAgent/AbstractDevice.php b/library/Zend/Http/UserAgent/AbstractDevice.php
index 62e031ac25..75d057f1cf 100644
--- a/library/Zend/Http/UserAgent/AbstractDevice.php
+++ b/library/Zend/Http/UserAgent/AbstractDevice.php
@@ -509,7 +509,9 @@ public static function extractFromUserAgent($userAgent)
                 }
                 $result['browser_version'] = '??';
             }
-        } elseif ($product == 'mozilla' && $result['browser_version'] < 5.0) {
+        } elseif ($product == 'mozilla' && isset($result['browser_version'])
+                  && $result['browser_version'] < 5.0
+        ) {
             // handles the real Mozilla (or old Netscape if version < 5.0)
             $result['browser_name'] = 'Netscape';
         }
diff --git a/tests/Zend/Http/UserAgent/AbstractDeviceTest.php b/tests/Zend/Http/UserAgent/AbstractDeviceTest.php
index 92ba4c14de..542c1d45c2 100644
--- a/tests/Zend/Http/UserAgent/AbstractDeviceTest.php
+++ b/tests/Zend/Http/UserAgent/AbstractDeviceTest.php
@@ -10128,4 +10128,14 @@ public function testOperaOnHtcHd2UserAgentShouldNotResultInNotices()
         $capabilities = Zend_Http_UserAgent_AbstractDevice::extractFromUserAgent($userAgent);
         $this->assertEquals('Opera', $capabilities['browser_name']);
     }
+
+    /**
+     * @group GH-550
+     */
+    public function testOnlyBrowserNameShouldNotResultInNotices()
+    {
+        $userAgent    = 'Mozilla';
+        $capabilities = Zend_Http_UserAgent_AbstractDevice::extractFromUserAgent($userAgent);
+        $this->assertEquals('Mozilla', $capabilities['browser_name']);
+    }
 }