diff --git a/src/urllib3/contrib/_appengine_environ.py b/src/urllib3/contrib/_appengine_environ.py
index 119efaeeb6..8765b907d7 100644
--- a/src/urllib3/contrib/_appengine_environ.py
+++ b/src/urllib3/contrib/_appengine_environ.py
@@ -6,7 +6,7 @@
 
 
 def is_appengine():
-    return "APPENGINE_RUNTIME" in os.environ
+    return is_local_appengine() or is_prod_appengine()
 
 
 def is_appengine_sandbox():
@@ -20,15 +20,15 @@ def is_appengine_sandbox():
 
 
 def is_local_appengine():
-    return is_appengine() and os.environ.get("SERVER_SOFTWARE", "").startswith(
-        "Development/"
-    )
+    return "APPENGINE_RUNTIME" in os.environ and os.environ.get(
+        "SERVER_SOFTWARE", ""
+    ).startswith("Development/")
 
 
 def is_prod_appengine():
-    return is_appengine() and os.environ.get("SERVER_SOFTWARE", "").startswith(
-        "Google App Engine/"
-    )
+    return "APPENGINE_RUNTIME" in os.environ and os.environ.get(
+        "SERVER_SOFTWARE", ""
+    ).startswith("Google App Engine/")
 
 
 def is_prod_appengine_mvms():