diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -50,7 +50,7 @@ void ShowNewGRFError()
 		SetDParamStr(3, c->filename);
 		SetDParam   (4, STR_JUST_RAW_STRING);
 		SetDParamStr(5, c->error->data);
-		for (uint i = 0; i < c->error->num_params; i++) {
+		for (uint i = 0; i < lengthof(c->error->param_value); i++) {
 			SetDParam(6 + i, c->error->param_value[i]);
 		}
 		ShowErrorMessage(STR_NEWGRF_ERROR_FATAL_POPUP, INVALID_STRING_ID, WL_CRITICAL);
@@ -67,7 +67,7 @@ static void ShowNewGRFInfo(const GRFConf
 		SetDParamStr(2, c->filename);
 		SetDParam   (3, STR_JUST_RAW_STRING);
 		SetDParamStr(4, c->error->data);
-		for (uint i = 0; i < c->error->num_params; i++) {
+		for (uint i = 0; i < lengthof(c->error->param_value); i++) {
 			SetDParam(5 + i, c->error->param_value[i]);
 		}
 		GetString(message, c->error->custom_message == NULL ? c->error->message : STR_JUST_RAW_STRING, lastof(message));