diff --git a/jwerty.js b/jwerty.js
index 8107bbf..34936f0 100644
--- a/jwerty.js
+++ b/jwerty.js
@@ -449,7 +449,7 @@
                 // For each property in the jwertyCode object, compare to `event`
                 for (var p in jwertyCode[n]) {
                     // ...except for jwertyCode.jwertyCombo...
-                    if (p !== 'jwertyCombo' && event[p] != jwertyCode[n][p]) returnValue = false;
+                    if (p !== 'jwertyCombo' && event[p] !== undefined && event[p] != jwertyCode[n][p]) returnValue = false;
                 }
                 // If this jwertyCode optional wasn't falsey, then we can return early.
                 if (returnValue !== false) return returnValue;
@@ -537,4 +537,4 @@
         KEYS: _keys
     };
 
-}(typeof global !== 'undefined' && global.window || this, (typeof module !== 'undefined' && module.exports ? module.exports : this)));
\ No newline at end of file
+}(typeof global !== 'undefined' && global.window || this, (typeof module !== 'undefined' && module.exports ? module.exports : this)));