diff --git a/MagickCore/option.h b/MagickCore/option.h
index cfd6596..a22855a 100644
--- a/MagickCore/option.h
+++ b/MagickCore/option.h
@@ -182,6 +182,7 @@
   DefineImageOption(ImageInfo *,const char *),
   DeleteImageOption(ImageInfo *,const char *),
   IsCommandOption(const char *),
+  IsOptionMember(const char *,const char *),
   ListCommandOptions(FILE *,const CommandOption,ExceptionInfo *),
   SetImageOption(ImageInfo *,const char *,const char *);