diff --git a/src/libostree/ostree-repo.c b/src/libostree/ostree-repo.c
index a77a5025..f5719890 100644
--- a/src/libostree/ostree-repo.c
+++ b/src/libostree/ostree-repo.c
@@ -2361,7 +2361,7 @@ gboolean
 ostree_repo_query_object_storage_size (OstreeRepo           *self,
                                        OstreeObjectType      objtype,
                                        const char           *sha256, 
-                                       gsize                *out_size,
+                                       guint64              *out_size,
                                        GCancellable         *cancellable,
                                        GError              **error)
 {
diff --git a/src/libostree/ostree-repo.h b/src/libostree/ostree-repo.h
index 54347670..a5ad7413 100644
--- a/src/libostree/ostree-repo.h
+++ b/src/libostree/ostree-repo.h
@@ -216,7 +216,7 @@ gboolean ostree_repo_load_object_stream (OstreeRepo         *self,
 gboolean      ostree_repo_query_object_storage_size (OstreeRepo           *self,
                                                      OstreeObjectType      objtype,
                                                      const char           *sha256, 
-                                                     gsize                *out_size,
+                                                     guint64              *out_size,
                                                      GCancellable         *cancellable,
                                                      GError              **error);