diff --git a/MacPass/MPKeyMapper.m b/MacPass/MPKeyMapper.m
index f638e3ab..669ff82a 100644
--- a/MacPass/MPKeyMapper.m
+++ b/MacPass/MPKeyMapper.m
@@ -33,6 +33,9 @@ uint16_t const kMPUnknownKeyCode = UINT16_MAX;
 }
 
 + (NSString *)stringForModifiedKey:(MPModifiedKey)modifiedKey {
+  if(modifiedKey.keyCode == kMPUnknownKeyCode) {
+    return nil;
+  }
   TISInputSourceRef currentKeyboard = TISCopyCurrentKeyboardInputSource();
   CFDataRef layoutData = TISGetInputSourceProperty(currentKeyboard,kTISPropertyUnicodeKeyLayoutData);