diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index 8d24915359..1cd9f94718 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -504,6 +504,8 @@ whatis(Node *n)
 			return Wlitbool;
 		case CTSTR:
 			return Wlitstr;
+		case CTNIL:
+			return Wlitnil;	// not used
 		}
 		return Wtunkn;
 	}