diff --git a/httpx/_client.py b/httpx/_client.py
index 4110fd7d96..e4b212b4ac 100644
--- a/httpx/_client.py
+++ b/httpx/_client.py
@@ -89,10 +89,10 @@ def trust_env(self) -> bool:
         return self._trust_env
 
     def _get_proxy_map(
-        self, proxies: typing.Optional[ProxiesTypes], trust_env: bool,
+        self, proxies: typing.Optional[ProxiesTypes], allow_env_proxies: bool,
     ) -> typing.Dict[str, typing.Optional[Proxy]]:
         if proxies is None:
-            if trust_env:
+            if allow_env_proxies:
                 return {
                     key: None if url is None else Proxy(url=url)
                     for key, url in get_environment_proxies().items()
@@ -473,7 +473,8 @@ def __init__(
             )
             limits = pool_limits
 
-        proxy_map = self._get_proxy_map(proxies, trust_env)
+        allow_env_proxies = trust_env and app is None and transport is None
+        proxy_map = self._get_proxy_map(proxies, allow_env_proxies)
 
         self._transport = self._init_transport(
             verify=verify,
@@ -1003,7 +1004,8 @@ def __init__(
             )
             limits = pool_limits
 
-        proxy_map = self._get_proxy_map(proxies, trust_env)
+        allow_env_proxies = trust_env and app is None and transport is None
+        proxy_map = self._get_proxy_map(proxies, allow_env_proxies)
 
         self._transport = self._init_transport(
             verify=verify,