diff --git a/src/builtins.h b/src/builtins.h
index f5f4676a5..1bfe32ce0 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -270,7 +270,7 @@ inline static bool START_FUNCTION(query *q)
 	if (q->eval)
 		return true;
 
-	if (!q->st.m->flags.unknown == 0)
+	if (!q->st.m->flags.unknown)
 		return throw_error(q, q->st.curr_cell, q->st.curr_frame, "existence_error", "procedure");
 
 	return false;