diff --git a/src/BOPCol/BOPCol_Parallel.hxx b/src/BOPCol/BOPCol_Parallel.hxx
index 2204a0cb43..efea73fc69 100644
--- a/src/BOPCol/BOPCol_Parallel.hxx
+++ b/src/BOPCol/BOPCol_Parallel.hxx
@@ -87,7 +87,7 @@ class BOPCol_ContextFunctor
     static Standard_Integer HashCode(const Standard_ThreadId theKey,
                                      const Standard_Integer  Upper)
     {
-      return ::HashCode(theKey, Upper);
+      return ::HashCode((Standard_Size)theKey, Upper);
     }
 
     static Standard_Boolean IsEqual(const Standard_ThreadId theKey1,