diff --git a/src/libostree/ostree-repo-private.h b/src/libostree/ostree-repo-private.h
index ceed4711..adf5ec2b 100644
--- a/src/libostree/ostree-repo-private.h
+++ b/src/libostree/ostree-repo-private.h
@@ -130,7 +130,7 @@ gboolean
 _ostree_repo_file_replace_contents (OstreeRepo    *self,
                                     int            dfd,
                                     const char    *path,
-                                    guint8        *buf,
+                                    const guint8  *buf,
                                     gsize          len,
                                     GCancellable  *cancellable,
                                     GError       **error);
diff --git a/src/libostree/ostree-repo.c b/src/libostree/ostree-repo.c
index b27fcce8..5215e665 100644
--- a/src/libostree/ostree-repo.c
+++ b/src/libostree/ostree-repo.c
@@ -1509,7 +1509,7 @@ gboolean
 _ostree_repo_file_replace_contents (OstreeRepo    *self,
                                     int            dfd,
                                     const char    *path,
-                                    guint8        *buf,
+                                    const guint8   *buf,
                                     gsize          len,
                                     GCancellable  *cancellable,
                                     GError       **error)