diff --git a/letsencrypt/__manifest__.py b/letsencrypt/__manifest__.py
index af8122a02..c478719a8 100644
--- a/letsencrypt/__manifest__.py
+++ b/letsencrypt/__manifest__.py
@@ -18,6 +18,6 @@
     "post_init_hook": "post_init_hook",
     "installable": True,
     "external_dependencies": {
-        "python": ["acme", "cryptography", "dnspython", "josepy"]
+        "python": ["acme<2.0.0", "cryptography", "dnspython", "josepy"]
     },
 }
diff --git a/requirements.txt b/requirements.txt
index 7f1c55ebc..0c497052a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 # generated from manifests external_dependencies
-acme
+acme<2.0.0
 astor
 cryptography
 dataclasses