diff --git a/pkgs/stdenv/generic/setup-new.sh b/pkgs/stdenv/generic/setup-new.sh
index 65baa0ecff2..2561399695c 100644
--- a/pkgs/stdenv/generic/setup-new.sh
+++ b/pkgs/stdenv/generic/setup-new.sh
@@ -511,7 +511,7 @@ unpackPhase() {
     # Find the source directory.
     if test -n "$setSourceRoot"; then
         eval "$setSourceRoot"
-    else
+    elif test -z "$sourceRoot"; then
         sourceRoot=
         for i in *; do
             if test -d "$i"; then