diff --git a/src/script/api/script_newgrf.cpp b/src/script/api/script_newgrf.cpp
--- a/src/script/api/script_newgrf.cpp
+++ b/src/script/api/script_newgrf.cpp
@@ -24,9 +24,9 @@ ScriptNewGRFList::ScriptNewGRFList()
 	}
 }
 
-/* static */ bool ScriptNewGRF::IsLoaded(uint32 grfid)
+/* static */ bool ScriptNewGRF::IsLoaded(SQInteger grfid)
 {
-	grfid = BSWAP32(grfid); // Match people's expectations.
+	grfid = BSWAP32(GB(grfid, 0, 32)); // Match people's expectations.
 
 	for (auto c = _grfconfig; c != nullptr; c = c->next) {
 		if (!HasBit(c->flags, GCF_STATIC) && c->ident.grfid == grfid) {
@@ -37,9 +37,9 @@ ScriptNewGRFList::ScriptNewGRFList()
 	return false;
 }
 
-/* static */ uint32 ScriptNewGRF::GetVersion(uint32 grfid)
+/* static */ SQInteger ScriptNewGRF::GetVersion(SQInteger grfid)
 {
-	grfid = BSWAP32(grfid); // Match people's expectations.
+	grfid = BSWAP32(GB(grfid, 0, 32)); // Match people's expectations.
 
 	for (auto c = _grfconfig; c != nullptr; c = c->next) {
 		if (!HasBit(c->flags, GCF_STATIC) && c->ident.grfid == grfid) {
@@ -50,9 +50,9 @@ ScriptNewGRFList::ScriptNewGRFList()
 	return 0;
 }
 
-/* static */ char *ScriptNewGRF::GetName(uint32 grfid)
+/* static */ char *ScriptNewGRF::GetName(SQInteger grfid)
 {
-	grfid = BSWAP32(grfid); // Match people's expectations.
+	grfid = BSWAP32(GB(grfid, 0, 32)); // Match people's expectations.
 
 	for (auto c = _grfconfig; c != nullptr; c = c->next) {
 		if (!HasBit(c->flags, GCF_STATIC) && c->ident.grfid == grfid) {
diff --git a/src/script/api/script_newgrf.hpp b/src/script/api/script_newgrf.hpp
--- a/src/script/api/script_newgrf.hpp
+++ b/src/script/api/script_newgrf.hpp
@@ -34,7 +34,7 @@ public:
 	 * @param grfid The grfid to check.
 	 * @return True if and only if a NewGRF with the given grfid is loaded in the game.
 	 */
-	static bool IsLoaded(uint32 grfid);
+	static bool IsLoaded(SQInteger grfid);
 
 	/**
 	 * Get the version of a loaded NewGRF.
@@ -42,7 +42,7 @@ public:
 	 * @pre ScriptNewGRF::IsLoaded(grfid).
 	 * @return Version of the NewGRF or 0 if the NewGRF specifies no version.
 	 */
-	static uint32 GetVersion(uint32 grfid);
+	static SQInteger GetVersion(SQInteger grfid);
 
 	/**
 	 * Get the name of a loaded NewGRF.
@@ -50,7 +50,7 @@ public:
 	 * @pre ScriptNewGRF::IsLoaded(grfid).
 	 * @return The name of the NewGRF or null if no name is defined.
 	 */
-	static char *GetName(uint32 grfid);
+	static char *GetName(SQInteger grfid);
 };
 
 #endif /* SCRIPT_NEWGRF_HPP */