diff --git a/installer.py b/installer.py
index a5f8c9479..51f4c97d5 100644
--- a/installer.py
+++ b/installer.py
@@ -976,7 +976,7 @@ def run_extension_installer(folder):
     try:
         log.debug(f"Extension installer: {path_installer}")
         env = os.environ.copy()
-        env['PYTHONPATH'] = os.path.abspath(".")
+        env['PYTHONPATH'] = os.path.abspath(".") + ";" + env['PYTHONPATH']
         result = subprocess.run(f'"{sys.executable}" "{path_installer}"', shell=True, env=env, check=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, cwd=folder)
         txt = result.stdout.decode(encoding="utf8", errors="ignore")
         debug(f'Extension installer: file="{path_installer}" {txt}')