diff --git a/bin/complement b/bin/complement
index f1ac017d1..1c4281987 100755
--- a/bin/complement
+++ b/bin/complement
@@ -53,7 +53,7 @@ fi
 
 # The base docker image to use for complement tests
 # You can build the default with `docker build -t continuwuity:complement -f ./docker/complement.Dockerfile .`
-# after running `cargo build`. Only the debug binary is used.
+# after running `cargo build -p conduwuit --features openreg`. Only the debug binary is used.
 COMPLEMENT_BASE_IMAGE="${COMPLEMENT_BASE_IMAGE:-continuwuity:complement}"
 
 # Complement tests that are skipped due to flakiness/reliability issues or we don't implement such features and won't for a long time
@@ -99,7 +99,7 @@ fi
 
 if ! docker image inspect "$COMPLEMENT_BASE_IMAGE" > /dev/null 2>&1; then
     echo "Complement base image not found: $COMPLEMENT_BASE_IMAGE"
-    echo "Build it with: cargo build -p conduwuit && docker build -t $COMPLEMENT_BASE_IMAGE -f docker/complement.Dockerfile ."
+    echo "Build it with: cargo build -p conduwuit --features openreg && docker build -t $COMPLEMENT_BASE_IMAGE -f docker/complement.Dockerfile ."
     exit 1
 fi
 
diff --git a/docs/development/testing.mdx b/docs/development/testing.mdx
index 6a2568698..3e6aa0201 100644
--- a/docs/development/testing.mdx
+++ b/docs/development/testing.mdx
@@ -12,11 +12,14 @@ Install Git, Rust, Docker, Go, and `jq`. From this repository's root, build the
 server image and run the suite:
 
 ```bash
-cargo build -p conduwuit
+cargo build -p conduwuit --features openreg
 docker build -t continuwuity:complement -f docker/complement.Dockerfile .
 ./bin/complement
 ```
 
+The `openreg` feature is required: without it the server refuses the open
+registrations Complement uses to create test users, and almost every test fails.
+
 The run can take up to an hour. The runner writes the full Go test stream to
 `tests/test_results/complement/test_logs.jsonl` and a sorted pass/fail/skip
 summary to `tests/test_results/complement/test_results.jsonl`. It exits nonzero