diff --git a/src/newgrf_industries.cpp b/src/newgrf_industries.cpp
index 9e40f2f281..da74f58d34 100644
--- a/src/newgrf_industries.cpp
+++ b/src/newgrf_industries.cpp
@@ -523,7 +523,7 @@ bool CheckIfCallBackAllowsCreation(TileIndex tile, IndustryType type, uint itspe
 
 	/* Unlike the "normal" cases, not having a valid result means we allow
 	 * the building of the industry, as that's how it's done in TTDP. */
-	if (group == NULL || group->type != SGT_CALLBACK) return true;
+	if (group == NULL || group->type != SGT_CALLBACK || group->g.callback.result == 0x400) return true;
 
 	/* Copy some parameters from the registers to the error message text ref. stack */
 	SwitchToErrorRefStack();
@@ -531,7 +531,6 @@ bool CheckIfCallBackAllowsCreation(TileIndex tile, IndustryType type, uint itspe
 	SwitchToNormalRefStack();
 
 	switch (group->g.callback.result) {
-		case 0x400: return true;
 		case 0x401: _error_message = STR_0239_SITE_UNSUITABLE; break;
 		case 0x402: _error_message = STR_0317_CAN_ONLY_BE_BUILT_IN_RAINFOREST; break;
 		case 0x403: _error_message = STR_0318_CAN_ONLY_BE_BUILT_IN_DESERT; break;
diff --git a/src/newgrf_industrytiles.cpp b/src/newgrf_industrytiles.cpp
index 50bdcba4bf..bab9977f73 100644
--- a/src/newgrf_industrytiles.cpp
+++ b/src/newgrf_industrytiles.cpp
@@ -284,6 +284,7 @@ bool PerformIndustryTileSlopeCheck(TileIndex ind_base_tile, TileIndex ind_tile,
 	if (its->grf_prop.grffile->grf_version < 7) {
 		return callback_res != 0;
 	}
+	if (callback_res == 0x400) return true;
 
 	/* Copy some parameters from the registers to the error message text ref. stack */
 	SwitchToErrorRefStack();
@@ -291,7 +292,6 @@ bool PerformIndustryTileSlopeCheck(TileIndex ind_base_tile, TileIndex ind_tile,
 	SwitchToNormalRefStack();
 
 	switch (callback_res) {
-		case 0x400: return true;
 		case 0x401: _error_message = STR_0239_SITE_UNSUITABLE;                 return false;
 		case 0x402: _error_message = STR_0317_CAN_ONLY_BE_BUILT_IN_RAINFOREST; return false;
 		case 0x403: _error_message = STR_0318_CAN_ONLY_BE_BUILT_IN_DESERT;     return false;