diff --git a/src/macros.h b/src/macros.h
index 571fed0..8c0e04a 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -336,3 +336,6 @@
 	    (p) = NULL; \
 	} \
     } while (0)
+
+/* Wether a command index indicates a user command. */
+#define IS_USER_CMDIDX(idx) ((int)(idx) < 0)