diff --git a/third_party/nix/src/libstore/build.cc b/third_party/nix/src/libstore/build.cc
index e7a9ea45e..dcc3c7edc 100644
--- a/third_party/nix/src/libstore/build.cc
+++ b/third_party/nix/src/libstore/build.cc
@@ -2490,7 +2490,7 @@ void DerivationGoal::initTmpDir() {
         env[i.first] = i.second;
       } else {
         auto hash = hashString(htSHA256, i.first);
-        std::string fn = ".attr-" + hash.to_string();
+        std::string fn = ".attr-" + hash.to_string(Base32, false);
         Path p = tmpDir + "/" + fn;
         writeFile(p, rewriteStrings(i.second, inputRewrites));
         chownToBuilder(p);
diff --git a/third_party/nix/tests/pass-as-file.sh b/third_party/nix/tests/pass-as-file.sh
index 3dfe10baa..2c0bc5031 100644
--- a/third_party/nix/tests/pass-as-file.sh
+++ b/third_party/nix/tests/pass-as-file.sh
@@ -10,6 +10,7 @@ mkDerivation {
   passAsFile = [ \"foo\" ];
   foo = [ \"xyzzy\" ];
   builder = builtins.toFile \"builder.sh\" ''
+    [ \"\$(basename \$fooPath)\" = .attr-1bp7cri8hplaz6hbz0v4f0nl44rl84q1sg25kgwqzipzd1mv89ic ]
     [ \"\$(cat \$fooPath)\" = xyzzy ]
     touch \$out
   '';