diff --git a/changelog.d/11625.misc b/changelog.d/11625.misc
new file mode 100644
index 000000000000..82ee78e72489
--- /dev/null
+++ b/changelog.d/11625.misc
@@ -0,0 +1 @@
+Work around a build problem on Debian Buster.
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 7d26954244ea..13fb69460ea9 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -50,7 +50,8 @@
 REQUIREMENTS = [
     # we use the TYPE_CHECKER.redefine method added in jsonschema 3.0.0
     "jsonschema>=3.0.0",
-    "frozendict>=1",
+    # frozendict 2.1.2 is broken on Debian 10: https://github.com/Marco-Sulla/python-frozendict/issues/41
+    "frozendict>=1,<2.1.2",
     "unpaddedbase64>=1.1.0",
     "canonicaljson>=1.4.0",
     # we use the type definitions added in signedjson 1.1.