diff --git a/pkgs/build-support/release/source-tarball.nix b/pkgs/build-support/release/source-tarball.nix
index 85d0b29f5b7..887bfb3125c 100644
--- a/pkgs/build-support/release/source-tarball.nix
+++ b/pkgs/build-support/release/source-tarball.nix
@@ -9,7 +9,7 @@
 , versionSuffix ? 
     if officialRelease
     then ""
-    else if src ? rev then "pre${toString src.rev}" else ""
+    else "pre${toString (src.rev or src.revCount or "")}"
 , src, stdenv, autoconf, automake, libtool
 , ... } @ args: