diff --git a/dlls/dinput/device.c b/dlls/dinput/device.c
index cf911531b52..c0f15ff26c6 100644
--- a/dlls/dinput/device.c
+++ b/dlls/dinput/device.c
@@ -510,7 +510,7 @@ int id_to_object(LPCDIDATAFORMAT df, int id)
     return -1;
 }
 
-int id_to_offset(const DataFormat *df, int id)
+static int id_to_offset(const DataFormat *df, int id)
 {
     int obj = id_to_object(df->wine_df, id);
 
diff --git a/dlls/dinput/device_private.h b/dlls/dinput/device_private.h
index d62e32ef97f..43b28c99fc2 100644
--- a/dlls/dinput/device_private.h
+++ b/dlls/dinput/device_private.h
@@ -81,7 +81,6 @@ extern void release_DataFormat(DataFormat *df) ;
 extern void queue_event(LPDIRECTINPUTDEVICE8A iface, int inst_id, DWORD data, DWORD time, DWORD seq);
 /* Helper functions to work with data format */
 extern int id_to_object(LPCDIDATAFORMAT df, int id);
-extern int id_to_offset(const DataFormat *df, int id);
 extern int find_property(const DataFormat *df, LPCDIPROPHEADER ph);
 
 /* Common joystick stuff */