1 files changed, 4 insertions, 0 deletions
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index b5555fbba9..5d087ee26b 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -79,6 +79,10 @@ CONDITIONAL_REQUIREMENTS = {
     # ConsentResource uses select_autoescape, which arrived in jinja 2.9
     "resources.consent": ["Jinja2>=2.9"],
 
+    # ACME support is required to provision TLS certificates from authorities
+    # that use the protocol, such as Let's Encrypt.
+    "acme": ["txacme>=0.9.2"],
+
     "saml2": ["pysaml2>=4.5.0"],
     "url_preview": ["lxml>=3.5.0"],
     "test": ["mock>=2.0", "parameterized"],