diff --git a/packages/core/src/material-library.ts b/packages/core/src/material-library.ts
index ca1ab1b93..074b07e5f 100644
--- a/packages/core/src/material-library.ts
+++ b/packages/core/src/material-library.ts
@@ -4187,13 +4187,14 @@ export function toSceneMaterialRef(id: string) {
 }
 
 export function getLibraryMaterialIdFromRef(materialRef?: string | null) {
-  if (!materialRef) return null
+  if (typeof materialRef !== 'string') return null
   if (!materialRef.startsWith(LIBRARY_MATERIAL_REF_PREFIX)) return null
   return materialRef.slice(LIBRARY_MATERIAL_REF_PREFIX.length)
 }
 
 export function getSceneMaterialIdFromRef(materialRef?: string | null): string | null {
-  if (!materialRef?.startsWith(SCENE_MATERIAL_REF_PREFIX)) return null
+  if (typeof materialRef !== 'string') return null
+  if (!materialRef.startsWith(SCENE_MATERIAL_REF_PREFIX)) return null
   return materialRef.slice(SCENE_MATERIAL_REF_PREFIX.length)
 }