diff --git a/auto_firmware_version.py b/auto_firmware_version.py
index f3f10702..4e122efc 100644
--- a/auto_firmware_version.py
+++ b/auto_firmware_version.py
@@ -11,7 +11,7 @@ installed_pkgs = {pkg.key for pkg in pkg_resources.working_set}
 missing_pkgs = required_pkgs - installed_pkgs
 
 if missing_pkgs:
-    env.Execute('$PYTHONEXE -m pip install dulwich --global-option="--pure"')
+    env.Execute('"$PYTHONEXE" -m pip install dulwich --global-option="--pure"')
 
 from dulwich import porcelain