diff --git a/dlls/wined3d/device.c b/dlls/wined3d/device.c
index 4509d932dbf..20bf808b816 100644
--- a/dlls/wined3d/device.c
+++ b/dlls/wined3d/device.c
@@ -4613,7 +4613,7 @@ HRESULT CDECL wined3d_device_set_npatch_mode(struct wined3d_device *device, floa
     return WINED3D_OK;
 }
 
-float CDECL wined3d_device_get_npatch_mode(struct wined3d_device *device)
+float CDECL wined3d_device_get_npatch_mode(const struct wined3d_device *device)
 {
     static BOOL warned;
 
diff --git a/include/wine/wined3d.h b/include/wine/wined3d.h
index 92d7d4d2bb9..e4664003cd9 100644
--- a/include/wine/wined3d.h
+++ b/include/wine/wined3d.h
@@ -2224,7 +2224,7 @@ HRESULT __cdecl wined3d_device_get_index_buffer(const struct wined3d_device *dev
 HRESULT __cdecl wined3d_device_get_light(const struct wined3d_device *device, UINT light_idx, WINED3DLIGHT *light);
 HRESULT __cdecl wined3d_device_get_light_enable(const struct wined3d_device *device, UINT light_idx, BOOL *enable);
 HRESULT __cdecl wined3d_device_get_material(const struct wined3d_device *device, WINED3DMATERIAL *material);
-float __cdecl wined3d_device_get_npatch_mode(struct wined3d_device *device);
+float __cdecl wined3d_device_get_npatch_mode(const struct wined3d_device *device);
 struct wined3d_shader * __cdecl wined3d_device_get_pixel_shader(const struct wined3d_device *device);
 void __cdecl wined3d_device_get_primitive_type(const struct wined3d_device *device,
         WINED3DPRIMITIVETYPE *primitive_topology);