diff --git a/lightningd/jsonrpc_errors.h b/lightningd/jsonrpc_errors.h
index 0258bcf34..1ba1ca21f 100644
--- a/lightningd/jsonrpc_errors.h
+++ b/lightningd/jsonrpc_errors.h
@@ -15,7 +15,9 @@
  * with a specific error code, and then removed.
  */
 #define LIGHTNINGD                      -1
-#define LIGHTNINGD_INTERNAL             -2
+
+/* Developer error in the parameters to param() call */
+#define PARAM_DEV_ERROR                 -2
 
 /* Errors from `pay`, `sendpay`, or `waitsendpay` commands */
 #define PAY_IN_PROGRESS			200
diff --git a/lightningd/param.c b/lightningd/param.c
index 3653f6e1c..a2c7f43be 100644
--- a/lightningd/param.c
+++ b/lightningd/param.c
@@ -284,7 +284,7 @@ static bool param_arr(struct command *cmd, const char *buffer,
 {
 #if DEVELOPER
 	if (!check_params(params)) {
-		command_fail(cmd, LIGHTNINGD_INTERNAL, "programmer error");
+		command_fail(cmd, PARAM_DEV_ERROR, "programmer error");
 		return false;
 	}
 #endif
@@ -312,8 +312,8 @@ bool param(struct command *cmd, const char *buffer,
 		void *arg = va_arg(ap, void *);
 		size_t argsize = va_arg(ap, size_t);
 		if  (!param_add(&params, name, required, cb, arg, argsize)) {
-			command_fail(cmd, LIGHTNINGD_INTERNAL,
-				     "programmer error");
+			command_fail(cmd, PARAM_DEV_ERROR, "programmer error");
+			va_end(ap);
 			return false;
 		}
 	}