diff --git a/Objects/stringlib/formatter.h b/Objects/stringlib/formatter.h
index 61ca12b..9cbd2cc 100644
--- a/Objects/stringlib/formatter.h
+++ b/Objects/stringlib/formatter.h
@@ -248,6 +248,7 @@
         case 'G':
         case '%':
         case 'F':
+        case '\0':
             /* These are allowed. See PEP 378.*/
             break;
         default: