diff --git a/src/corelib/global/q20functional.h b/src/corelib/global/q20functional.h
index 787b3ec035..13e6c9e090 100644
--- a/src/corelib/global/q20functional.h
+++ b/src/corelib/global/q20functional.h
@@ -23,6 +23,8 @@
 // We mean it.
 //
 
+#include <functional>
+
 QT_BEGIN_NAMESPACE
 
 namespace q20 {