diff --git a/dix/property.c b/dix/property.c
index ff1d6693b..94ef5a0ec 100644
--- a/dix/property.c
+++ b/dix/property.c
@@ -253,7 +253,7 @@ ProcChangeProperty(ClientPtr client)
 int
 dixChangeWindowProperty(ClientPtr pClient, WindowPtr pWin, Atom property,
                         Atom type, int format, int mode, unsigned long len,
-                        void *value, Bool sendevent)
+                        const void *value, Bool sendevent)
 {
     PropertyPtr pProp;
     PropertyRec savedProp;
diff --git a/include/property.h b/include/property.h
index d7ccff344..6ee8a8398 100644
--- a/include/property.h
+++ b/include/property.h
@@ -72,7 +72,7 @@ extern _X_EXPORT int dixChangeWindowProperty(ClientPtr pClient,
                                              int format,
                                              int mode,
                                              unsigned long len,
-                                             void *value,
+                                             const void *value,
                                              Bool sendevent);
 
 extern _X_EXPORT int DeleteProperty(ClientPtr /*client */ ,