diff --git a/src/compositor/region-utils.c b/src/compositor/region-utils.c
index 081f8a906..4f5a2346a 100644
--- a/src/compositor/region-utils.c
+++ b/src/compositor/region-utils.c
@@ -376,7 +376,7 @@ meta_make_border_region (cairo_region_t *region,
 }
 
 cairo_region_t *
-meta_region_transform (cairo_region_t       *region,
+meta_region_transform (const cairo_region_t *region,
                        MetaMonitorTransform  transform,
                        int                   width,
                        int                   height)
diff --git a/src/compositor/region-utils.h b/src/compositor/region-utils.h
index 745021b5b..298c5540e 100644
--- a/src/compositor/region-utils.h
+++ b/src/compositor/region-utils.h
@@ -106,7 +106,7 @@ cairo_region_t * meta_make_border_region (cairo_region_t *region,
                                           int             y_amount,
                                           gboolean        flip);
 
-cairo_region_t * meta_region_transform (cairo_region_t       *region,
+cairo_region_t * meta_region_transform (const cairo_region_t *region,
                                         MetaMonitorTransform  transform,
                                         int                   width,
                                         int                   height);