diff --git a/code/Material/MaterialSystem.cpp b/code/Material/MaterialSystem.cpp
index aa3df9ac2..befdb43d2 100644
--- a/code/Material/MaterialSystem.cpp
+++ b/code/Material/MaterialSystem.cpp
@@ -504,7 +504,7 @@ aiReturn aiMaterial::AddBinaryProperty (const void* pInput,
     pcNew->mData = new char[pSizeInBytes];
     memcpy (pcNew->mData,pInput,pSizeInBytes);
 
-    pcNew->mKey.length = ::strlen(pKey);
+    pcNew->mKey.length = (ai_uint32)::strlen(pKey);
     ai_assert ( MAXLEN > pcNew->mKey.length);
     strcpy( pcNew->mKey.data, pKey );