diff --git a/scripts/test_dependency_invalidation.sh b/scripts/test_dependency_invalidation.sh
index bb06022..a81fe4c 100755
--- a/scripts/test_dependency_invalidation.sh
+++ b/scripts/test_dependency_invalidation.sh
@@ -14,6 +14,7 @@ cache_dir=""
 mutation_file="/tmp/uce-dependency-mutation-$$"
 post_body="/tmp/uce-dependency-post-body-$$"
 post_headers="/tmp/uce-dependency-post-headers-$$"
+lock_ready_file="/tmp/uce-dependency-lock-ready-$$"
 http_host="${UCE_TEST_HTTP_HOST:-uce.openfu.com}"
 
 cleanup() {
@@ -21,7 +22,7 @@ cleanup() {
 	if [[ -n "$cache_dir" ]]; then
 		rm -rf "$cache_dir"
 	fi
-	rm -f "$mutation_file" "$post_body" "$post_headers"
+	rm -f "$mutation_file" "$post_body" "$post_headers" "$lock_ready_file"
 }
 trap cleanup EXIT
 mkdir -p "$source_dir"
@@ -108,10 +109,22 @@ child_wasm="$cache_dir/child.uce.wasm"
 	exec 9>"$child_wasm.lock"
 	flock 8
 	flock 9
+	: >"$lock_ready_file"
 	sleep 3
 ) &
 rebuild_lock_pid=$!
-sleep 0.2
+deadline=$((SECONDS + 5))
+while [[ ! -e "$lock_ready_file" && $SECONDS -lt $deadline ]]; do
+	if ! kill -0 "$rebuild_lock_pid" 2>/dev/null; then
+		echo "test rebuild lock process exited before acquiring locks" >&2
+		exit 1
+	fi
+	sleep 0.05
+done
+if [[ ! -e "$lock_ready_file" ]]; then
+	echo "test rebuild lock process did not acquire locks before deadline" >&2
+	exit 1
+fi
 sed -i 's/dependency-marker-b/dependency-marker-d/' "$source_dir/child.uce"
 started_at=$(date +%s%N)
 http_during_lock=$(http_marker)