diff --git a/merge-check-typescript.sh b/merge-check-typescript.sh
index de5aa5a0..4a66f9da 100644
--- a/merge-check-typescript.sh
+++ b/merge-check-typescript.sh
@@ -29,12 +29,12 @@ if [ ! -f "$tsc" ]; then
 	exit 1
 fi
 
-# The modules the change reaches, as merge-check.sh reads them (hq ADR 0238).
-if [ -n "${MESH_CHECK_MODULES:-}" ]; then
-	touched=$(printf '%s\n' "$MESH_CHECK_MODULES" | tr ',' '\n' | sed -e 's#^modules/##' -e '/\//d' | sort -u)
-else
-	touched=$(printf '%s\n' "${MESH_CHECK_CHANGED:-}" | tr ',' '\n' | sed -n 's#^modules/\([^/]*\)/.*#\1#p' | sort -u)
-fi
+# The modules the change reaches: the planner's answer (hq ADR 0238), and every module a changed file is in —
+# a change to a module's tests alone moves no build (hq ADR 0267), and its tests must still run.
+touched=$({
+	printf '%s\n' "${MESH_CHECK_MODULES:-}" | tr ',' '\n' | sed -e 's#^modules/##' -e '/\//d'
+	printf '%s\n' "${MESH_CHECK_CHANGED:-}" | tr ',' '\n' | sed -n 's#^modules/\([^/]*\)/.*#\1#p'
+} | sed '/^$/d' | sort -u)
 
 work=$(mktemp -d)
 trap 'rm -rf "$work"' EXIT