diff --git a/transaction.h b/transaction.h
index a1070e0d..e8610b1d 100644
--- a/transaction.h
+++ b/transaction.h
@@ -34,6 +34,7 @@ btrfs_start_transaction(struct btrfs_root *root, int num_blocks)
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_trans_handle *h = malloc(sizeof(*h));
 
+	BUG_ON(!h);
 	BUG_ON(root->commit_root);
 	BUG_ON(fs_info->running_transaction);
 	fs_info->running_transaction = h;