diff --git a/httpcore/_async/http_proxy.py b/httpcore/_async/http_proxy.py
index d24e88c2a..ee64d3132 100644
--- a/httpcore/_async/http_proxy.py
+++ b/httpcore/_async/http_proxy.py
@@ -101,6 +101,7 @@ def create_connection(self, origin: Origin) -> AsyncConnectionInterface:
         if origin.scheme == b"http":
             return AsyncForwardHTTPConnection(
                 proxy_origin=self._proxy_url.origin,
+                proxy_headers=self._proxy_headers,
                 keepalive_expiry=self._keepalive_expiry,
                 network_backend=self._network_backend,
             )
diff --git a/httpcore/_sync/http_proxy.py b/httpcore/_sync/http_proxy.py
index ac07273a4..d00b4d4f0 100644
--- a/httpcore/_sync/http_proxy.py
+++ b/httpcore/_sync/http_proxy.py
@@ -101,6 +101,7 @@ def create_connection(self, origin: Origin) -> ConnectionInterface:
         if origin.scheme == b"http":
             return ForwardHTTPConnection(
                 proxy_origin=self._proxy_url.origin,
+                proxy_headers=self._proxy_headers,
                 keepalive_expiry=self._keepalive_expiry,
                 network_backend=self._network_backend,
             )