diff --git a/src/corelib/global/qcompare.h b/src/corelib/global/qcompare.h
index 9dd244c8f92..fb5a40f0529 100644
--- a/src/corelib/global/qcompare.h
+++ b/src/corelib/global/qcompare.h
@@ -62,6 +62,9 @@ constexpr O reversed(O o) noexcept
 
 namespace Qt {
 
+class weak_ordering;
+class strong_ordering;
+
 class partial_ordering
 {
 public: