diff --git a/Cargo.toml b/Cargo.toml
index 4bf5a7387..339004d12 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -358,6 +358,7 @@ features = [
     "markdown",
     "ring-compat",
     "compat-upload-signatures",
+    "compat-optional-txn-pdus",
     "unstable-msc2448",
     "unstable-msc2666",
     "unstable-msc2867",