diff --git a/protonfixes_test.py b/protonfixes_test.py
index 83ce91b9..e8d4b71a 100644
--- a/protonfixes_test.py
+++ b/protonfixes_test.py
@@ -192,8 +192,8 @@ def testGetGameNone(self):
         self.assertTrue('SteamGameId' not in os.environ, 'SteamGameId is set')
         self.assertTrue('UMU_ID' not in os.environ, 'UMU_ID is set')
         self.assertTrue('SteamAppId' not in os.environ, 'SteamAppId is set')
-        result = func()
-        self.assertFalse(result, 'None was not returned')
+        with self.assertRaises(SystemExit):
+            func()
 
     def testGetStoreNameZoom(self):
         """Pass zoomplatform as store name
diff --git a/util.py b/util.py
index ab5a0a33..8b56823b 100644
--- a/util.py
+++ b/util.py
@@ -85,9 +85,10 @@ def protondir() -> str:
     return os.path.dirname(sys.argv[0])
 
 
+@functools.lru_cache
 def protonprefix() -> str:
-    """Returns the wineprefix used by proton"""
-    return os.path.join(os.environ['STEAM_COMPAT_DATA_PATH'], 'pfx/')
+    """Returns wineprefix's path used by proton"""
+    return os.path.join(os.environ.get('STEAM_COMPAT_DATA_PATH', ''), 'pfx/')
 
 
 def protonnameversion() -> Optional[str]: