diff --git a/dix/dix_priv.h b/dix/dix_priv.h
index 1fbbf8ff2..56a2882bc 100644
--- a/dix/dix_priv.h
+++ b/dix/dix_priv.h
@@ -544,4 +544,14 @@ void ScreenRestructured(ScreenPtr pScreen)
  */
 int OtherClientGone(void *value, XID id);
 
+/*
+ * @brief check whether one window is parent of another
+ *
+ * @param parent    the alleged parent
+ * @param child     the alleged child
+ * @return TRUE if `child` is a child window of `parent`
+ */
+Bool IsParent(WindowPtr parent, WindowPtr child)
+    _X_ATTRIBUTE_NONNULL_ARG(1,2);
+
 #endif /* _XSERVER_DIX_PRIV_H */
diff --git a/include/dix.h b/include/dix.h
index 7c4ba4dc0..afbf7c1a6 100644
--- a/include/dix.h
+++ b/include/dix.h
@@ -231,10 +231,6 @@ SetVendorRelease(int release);
 
 /* events.c */
 
-extern _X_EXPORT Bool
-IsParent(WindowPtr /* maybeparent */ ,
-         WindowPtr /* child */ );
-
 extern _X_EXPORT void
 NoticeTime(const DeviceIntPtr dev,
            TimeStamp time);