diff --git a/docker/complement/conf/start_for_complement.sh b/docker/complement/conf/start_for_complement.sh
index e0cd275ff3..8ed28d11cb 100755
--- a/docker/complement/conf/start_for_complement.sh
+++ b/docker/complement/conf/start_for_complement.sh
@@ -6,7 +6,7 @@ set -e
 
 echo "Complement Synapse launcher"
 echo "  Args: $*"
-echo "  Env: SYNAPSE_COMPLEMENT_DATABASE=$SYNAPSE_COMPLEMENT_DATABASE SYNAPSE_COMPLEMENT_USE_WORKERS=$SYNAPSE_COMPLEMENT_USE_WORKERS SYNAPSE_COMPLEMENT_USE_ASYNCIO_REACTOR=$SYNAPSE_COMPLEMENT_USE_ASYNCIO_REACTOR SYNAPSE_USE_RUST_DRIVER=$SYNAPSE_USE_RUST_DRIVER"
+echo "  Env: SYNAPSE_COMPLEMENT_DATABASE=$SYNAPSE_COMPLEMENT_DATABASE SYNAPSE_COMPLEMENT_USE_WORKERS=$SYNAPSE_COMPLEMENT_USE_WORKERS SYNAPSE_COMPLEMENT_USE_ASYNCIO_REACTOR=$SYNAPSE_COMPLEMENT_USE_ASYNCIO_REACTOR SYNAPSE_USE_RUST_DRIVER=$SYNAPSE_USE_RUST_DRIVER SYNAPSE_RUST_STATE_RES=$SYNAPSE_RUST_STATE_RES"
 
 function log {
     d=$(printf '%(%Y-%m-%d %H:%M:%S)T,%.3s\n' ${EPOCHREALTIME/./ })
@@ -128,6 +128,13 @@ openssl x509 -req -in /conf/server.tls.csr \
 export SYNAPSE_TLS_CERT=/conf/server.tls.crt
 export SYNAPSE_TLS_KEY=/conf/server.tls.key
 
+# Resolve state in Rust (`experimental_features.rust_state_res`). This goes into
+# the shared config's `experimental_features`, as a config snippet with its own
+# `experimental_features` would replace the shared one.
+if [[ -n "$SYNAPSE_RUST_STATE_RES" ]]; then
+  sed -i "s/^experimental_features:$/experimental_features:\n  rust_state_res: $SYNAPSE_RUST_STATE_RES/" /conf/shared.yaml.j2
+fi
+
 # Add a directory for tests to add config overrides if they want
 mkdir --parents /conf/homeserver.d
 export _SYNAPSE_COMPLEMENT_EXTRA_CONFIG_DIR=/conf/homeserver.d
diff --git a/scripts-dev/complement.sh b/scripts-dev/complement.sh
index ccbbc7b924..6e2bf37e42 100755
--- a/scripts-dev/complement.sh
+++ b/scripts-dev/complement.sh
@@ -364,6 +364,12 @@ main() {
     export PASS_SYNAPSE_USE_RUST_DRIVER=true
   fi
 
+  if [[ -n "$RUST_STATE_RES" ]]; then
+    # Set `experimental_features.rust_state_res` (off, shadow or on). The Rust
+    # state resolution needs RUST_DRIVER=1.
+    export PASS_SYNAPSE_RUST_STATE_RES="$RUST_STATE_RES"
+  fi
+
   if [[ -n "$UNIX_SOCKETS" ]]; then
     # Enable full on Unix socket mode for Synapse, Redis and Postgresql
     export PASS_SYNAPSE_USE_UNIX_SOCKET=1