diff -up usermode-1.114-build/usermode-1.114/userhelper.c.fixnoargs usermode-1.114-build/usermode-1.114/userhelper.c
--- usermode-1.114-build/usermode-1.114/userhelper.c.fixnoargs	2025-07-09 00:13:58.800352637 +0200
+++ usermode-1.114-build/usermode-1.114/userhelper.c	2025-07-09 00:13:58.814677097 +0200
@@ -2397,6 +2397,12 @@ main(int argc, char **argv)
 		exit(ERR_INVALID_CALL);
 	}
 
+	if (!SHELL_FLAGS && !c_flag && !w_flag) {
+		debug_msg("userhelper: invalid call: "
+			"missing action argument\n");
+		exit(ERR_INVALID_CALL);
+	}
+
 	/* Determine which conversation function to use. */
 	if (t_flag) {
 		/* We were told to use text mode. */