diff --git a/src/libostree/ostree-repo-commit.c b/src/libostree/ostree-repo-commit.c
index 37be748b..7e1d707b 100644
--- a/src/libostree/ostree-repo-commit.c
+++ b/src/libostree/ostree-repo-commit.c
@@ -903,7 +903,7 @@ write_content_object (OstreeRepo         *self,
             return glnx_throw (error, "min-free-space-percent '%u%%' would be exceeded, %s more required",
                                self->min_free_space_percent, formatted_required);
           else
-            return glnx_throw (error, "min-free-space-size %luMB would be exceeded, %s more required",
+            return glnx_throw (error, "min-free-space-size %" G_GUINT64_FORMAT "MB would be exceeded, %s more required",
                                self->min_free_space_mb, formatted_required);
         }
       /* This is the main bit that needs mutex protection */
@@ -1617,7 +1617,7 @@ ostree_repo_prepare_transaction (OstreeRepo     *self,
             return glnx_throw (error, "min-free-space-percent '%u%%' would be exceeded, %s available",
                                self->min_free_space_percent, formatted_free);
           else
-            return glnx_throw (error, "min-free-space-size %luMB would be exceeded, %s available",
+            return glnx_throw (error, "min-free-space-size %" G_GUINT64_FORMAT "MB would be exceeded, %s available",
                                self->min_free_space_mb, formatted_free);
         }
       g_mutex_unlock (&self->txn_lock);