diff --git a/ioctl.h b/ioctl.h
index cdfb888..ad4372c 100644
--- a/ioctl.h
+++ b/ioctl.h
@@ -710,3 +710,3 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 		default:
-			return NULL;
+			return 0;
 	}