diff --git a/src/components/automations/automation-builder.tsx b/src/components/automations/automation-builder.tsx
index 677f62b..e2cba49 100644
--- a/src/components/automations/automation-builder.tsx
+++ b/src/components/automations/automation-builder.tsx
@@ -723,6 +723,18 @@ function KeywordMatchConfig({
   // when the trigger type changes, so the seed stays in sync.
   const [draft, setDraft] = useState(keywords.join(", "))
 
+  // Persist the default the <select> displays. The dropdown falls back to
+  // "contains" for display, but leaving it untouched would otherwise omit
+  // match_type from the saved config — and activation validation then
+  // rejected it (trigger.match_type). Seed once on mount; the component
+  // remounts when the trigger type changes, matching the keywords draft.
+  useEffect(() => {
+    if (config?.match_type == null) {
+      onChange({ ...config, match_type: "contains" })
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [])
+
   function commit() {
     const parsed = draft
       .split(",")
diff --git a/src/lib/automations/validate.test.ts b/src/lib/automations/validate.test.ts
index d7c54f5..75cae10 100644
--- a/src/lib/automations/validate.test.ts
+++ b/src/lib/automations/validate.test.ts
@@ -212,6 +212,12 @@ describe("validateTriggerForActivation", () => {
     expect(issues.map((i) => i.path)).toContain("trigger.match_type");
   });
 
+  it("accepts keyword_match with a missing match_type (defaults to contains)", () => {
+    expect(
+      validateTriggerForActivation("keyword_match", { keywords: ["hi"] }),
+    ).toEqual([]);
+  });
+
   it("requires schedule on time_based triggers", () => {
     expect(validateTriggerForActivation("time_based", {})).toEqual([
       { path: "trigger.schedule", message: "schedule is required" },
diff --git a/src/lib/automations/validate.ts b/src/lib/automations/validate.ts
index 707d685..6b652ec 100644
--- a/src/lib/automations/validate.ts
+++ b/src/lib/automations/validate.ts
@@ -154,7 +154,13 @@ export function validateTriggerForActivation(
     } else if (k.some((v) => typeof v !== 'string' || v.trim() === '')) {
       issues.push({ path: 'trigger.keywords', message: 'keywords cannot be empty strings' })
     }
-    if (cfg.match_type !== 'exact' && cfg.match_type !== 'contains') {
+    // A missing match_type defaults to "contains" at runtime (see
+    // automations/engine.ts and flows/engine.ts, which both read
+    // `match_type ?? "contains"`), so only an explicit, unrecognised
+    // value is invalid here. This keeps activation validation in step
+    // with the engine and with the builder's "Contains" default — an
+    // automation that shows the default in the UI must not be rejected.
+    if (cfg.match_type != null && cfg.match_type !== 'exact' && cfg.match_type !== 'contains') {
       issues.push({
         path: 'trigger.match_type',
         message: 'match type must be "exact" or "contains"',