diff --git a/src/newgrf_commons.h b/src/newgrf_commons.h
--- a/src/newgrf_commons.h
+++ b/src/newgrf_commons.h
@@ -218,7 +218,6 @@ public:
 
 	inline uint16 GetMaxMapping() const { return max_new_entities; }
 	inline uint16 GetMaxOffset() const { return max_offset; }
-	inline bool IsValidID(uint16 entity_id) const { return entity_overrides[entity_id] != invalid_ID; }
 };
 
 
diff --git a/src/saveload/newgrf_sl.cpp b/src/saveload/newgrf_sl.cpp
--- a/src/saveload/newgrf_sl.cpp
+++ b/src/saveload/newgrf_sl.cpp
@@ -30,7 +30,8 @@ static const SaveLoad _newgrf_mapping_de
 void Save_NewGRFMapping(const OverrideManagerBase &mapping)
 {
 	for (uint i = 0; i < mapping.GetMaxMapping(); i++) {
-		if (!mapping.IsValidID(i)) continue;
+		if (mapping.mapping_ID[i].grfid == 0 &&
+		    mapping.mapping_ID[i].entity_id == 0) continue;
 		SlSetArrayIndex(i);
 		SlObject(&mapping.mapping_ID[i], _newgrf_mapping_desc);
 	}