diff --git a/src/lookup_string_in_fixed_set.c b/src/lookup_string_in_fixed_set.c
index 01edc4e..57d455b 100644
--- a/src/lookup_string_in_fixed_set.c
+++ b/src/lookup_string_in_fixed_set.c
@@ -275,3 +275,11 @@ int _HIDDEN LookupStringInFixedSet(const unsigned char* graph,
 
 	return -1; /* No match */
 }
+
+/* prototype to skip warning with -Wmissing-prototypes */
+int _HIDDEN GetUtfMode(const unsigned char *graph, size_t length);
+
+int _HIDDEN GetUtfMode(const unsigned char *graph, size_t length)
+{
+	return length > 0 && graph[length - 1] < 0x80;
+}