diff --git a/ui/build/config.go b/ui/build/config.go
index 27ed8e9..a1b5bd4 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -115,6 +115,8 @@
 	// Tell python not to spam the source tree with .pyc files.
 	ret.environ.Set("PYTHONDONTWRITEBYTECODE", "1")
 
+	ret.environ.Set("TMPDIR", absPath(ctx, ret.TempDir()))
+
 	// Precondition: the current directory is the top of the source tree
 	if _, err := os.Stat(srcDirFileCheck); err != nil {
 		if os.IsNotExist(err) {