diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index d13b1c83f7..9037ea6380 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -272,6 +272,8 @@ static StringID MapGRFStringID(uint32 grfid, StringID str)
 	TEXID_TO_STRINGID(0x482A, 0x483B, STR_482A_PRODUCTION_LAST_MONTH);
 #undef TEXTID_TO_STRINGID
 
+	if (str == STR_NULL) return STR_EMPTY;
+
 	return str;
 }