diff --git a/CHANGELOG.md b/CHANGELOG.md
index 84b8709cbe..c895f68814 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## Unreleased
+
+### Fixed
+
+* Respect the `http1` argument while configuring proxy transports. (#3023)
+
 ## 0.26.0 (20th December, 2023)
 
 ### Added
diff --git a/httpx/_client.py b/httpx/_client.py
index 2813a84f01..422bf0fad8 100644
--- a/httpx/_client.py
+++ b/httpx/_client.py
@@ -1493,6 +1493,7 @@ def _init_proxy_transport(
         return AsyncHTTPTransport(
             verify=verify,
             cert=cert,
+            http1=http1,
             http2=http2,
             limits=limits,
             trust_env=trust_env,