diff --git a/spacy/morphology.pyx b/spacy/morphology.pyx
index 399ce406e..3e369fb3e 100644
--- a/spacy/morphology.pyx
+++ b/spacy/morphology.pyx
@@ -42,7 +42,7 @@ def _normalize_props(props):
         elif isinstance(key, (int, str)) and isinstance(value, (int, str)):
             out[key] = value
         else:
-            warnings.warn(Warnings.100.format(feature={key: value}))
+            warnings.warn(Warnings.W100.format(feature={key: value}))
     return out