diff --git a/addons/misra.py b/addons/misra.py
index 59c1b52cf..6ff5a5f13 100755
--- a/addons/misra.py
+++ b/addons/misra.py
@@ -358,9 +358,12 @@ C99_KEYWORDS = {
 
 
 def isKeyword(keyword, standard='c99'):
-    if standard == 'c99':
-        return C99_KEYWORDS
-    return keyword in C90_KEYWORDS
+    kw_set = {}
+    if standard == 'c89':
+        kw_set = C90_KEYWORDS
+    elif standard == 'c99':
+        kw_set = C99_KEYWORDS
+    return keyword in kw_set
 
 
 def getEssentialTypeCategory(expr):