diff --git a/CLAUDE.md b/CLAUDE.md
index 77c14ce6..be7b1d8b 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -70,6 +70,7 @@ PostgreSQL (Flyway): `cameleer-server-app/src/main/resources/db/migration/`
 - V11 — Outbound connections (outbound_connections table, enums)
 - V12 — Alerting tables (alert_rules, alert_rule_targets, alert_instances, alert_notifications, alert_reads, alert_silences)
 - V13 — alert_instances open-rule unique index (alert_instances_open_rule_uq partial index on rule_id WHERE state IN PENDING/FIRING/ACKNOWLEDGED)
+- V14 — Repair EXCHANGE_MATCH alert_rules persisted with fireMode=null (sets fireMode=PER_EXCHANGE + perExchangeLingerSeconds=300); paired with stricter `ExchangeMatchCondition` ctor that now rejects null fireMode.
 
 ClickHouse: `cameleer-server-app/src/main/resources/clickhouse/init.sql` (run idempotently on startup)
 
diff --git a/cameleer-server-app/src/main/resources/db/migration/V14__fix_null_firemode_alert_rules.sql b/cameleer-server-app/src/main/resources/db/migration/V14__fix_null_firemode_alert_rules.sql
new file mode 100644
index 00000000..dbe76313
--- /dev/null
+++ b/cameleer-server-app/src/main/resources/db/migration/V14__fix_null_firemode_alert_rules.sql
@@ -0,0 +1,19 @@
+-- V14 — Repair EXCHANGE_MATCH rules persisted with fireMode=null.
+-- Root cause: the rule editor wizard reset the condition payload on kind
+-- change without seeding a fireMode default, and the backend ctor allowed
+-- null to pass. Stricter ctor in ExchangeMatchCondition now rejects null
+-- fireMode — existing rows need to be repaired so startup doesn't fail
+-- deserialization and the evaluator stops NPE-looping on them.
+--
+-- Default to PER_EXCHANGE + perExchangeLingerSeconds=300 — the same default
+-- the UI now seeds when a user picks EXCHANGE_MATCH.
+UPDATE alert_rules
+   SET condition = jsonb_set(
+                     jsonb_set(condition, '{fireMode}', '"PER_EXCHANGE"', true),
+                     '{perExchangeLingerSeconds}',
+                     COALESCE(condition->'perExchangeLingerSeconds', '300'::jsonb),
+                     true
+                   ),
+       updated_at = now()
+ WHERE condition_kind = 'EXCHANGE_MATCH'
+   AND (condition->>'fireMode') IS NULL;
diff --git a/cameleer-server-core/src/main/java/com/cameleer/server/core/alerting/ExchangeMatchCondition.java b/cameleer-server-core/src/main/java/com/cameleer/server/core/alerting/ExchangeMatchCondition.java
index 0ea59eb0..e8a56cc8 100644
--- a/cameleer-server-core/src/main/java/com/cameleer/server/core/alerting/ExchangeMatchCondition.java
+++ b/cameleer-server-core/src/main/java/com/cameleer/server/core/alerting/ExchangeMatchCondition.java
@@ -14,6 +14,8 @@ public record ExchangeMatchCondition(
 ) implements AlertCondition {
 
     public ExchangeMatchCondition {
+        if (fireMode == null)
+            throw new IllegalArgumentException("fireMode is required (PER_EXCHANGE or COUNT_IN_WINDOW)");
         if (fireMode == FireMode.COUNT_IN_WINDOW && (threshold == null || windowSeconds == null))
             throw new IllegalArgumentException("COUNT_IN_WINDOW requires threshold + windowSeconds");
         if (fireMode == FireMode.PER_EXCHANGE && perExchangeLingerSeconds == null)
diff --git a/cameleer-server-core/src/test/java/com/cameleer/server/core/alerting/AlertConditionJsonTest.java b/cameleer-server-core/src/test/java/com/cameleer/server/core/alerting/AlertConditionJsonTest.java
index b17b056b..8ecf85f0 100644
--- a/cameleer-server-core/src/test/java/com/cameleer/server/core/alerting/AlertConditionJsonTest.java
+++ b/cameleer-server-core/src/test/java/com/cameleer/server/core/alerting/AlertConditionJsonTest.java
@@ -6,6 +6,7 @@ import java.util.List;
 import java.util.Map;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 class AlertConditionJsonTest {
 
@@ -43,6 +44,34 @@ class AlertConditionJsonTest {
         assertThat(((ExchangeMatchCondition) parsed).threshold()).isEqualTo(5);
     }
 
+    @Test
+    void exchangeMatchRejectsNullFireMode() {
+        assertThatThrownBy(() -> new ExchangeMatchCondition(
+                new AlertScope(null, null, null),
+                new ExchangeMatchCondition.ExchangeFilter("FAILED", Map.of()),
+                null, null, null, null))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("fireMode");
+    }
+
+    @Test
+    void exchangeMatchRejectsNullFireModeOnDeserialization() throws Exception {
+        String json = """
+            {
+              "kind": "EXCHANGE_MATCH",
+              "scope": {},
+              "filter": {"status": "FAILED", "attributes": {}},
+              "fireMode": null,
+              "threshold": null,
+              "windowSeconds": null,
+              "perExchangeLingerSeconds": null
+            }
+            """;
+        assertThatThrownBy(() -> om.readValue(json, AlertCondition.class))
+            .hasRootCauseInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("fireMode");
+    }
+
     @Test
     void roundtripAgentState() throws Exception {
         var c = new AgentStateCondition(new AlertScope("orders", null, null), "DEAD", 60);
diff --git a/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx b/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx
index a0c4cb1b..2d5c21f6 100644
--- a/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx
+++ b/ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx
@@ -14,10 +14,19 @@ export function ConditionStep({ form, setForm }: { form: FormState; setForm: (f:
     // Reset the condition payload so stale fields from a previous kind don't leak
     // into the save request. Preserve scope — it's managed on the scope step.
     const prev = form.condition as Record<string, unknown>;
+    const base: Record<string, unknown> = { kind, scope: prev.scope };
+    // EXCHANGE_MATCH must carry a fireMode — the backend ctor now rejects null.
+    // Seed PER_EXCHANGE + 300s linger so a user can save without touching every
+    // sub-field (matches what the form's Select displays by default).
+    if (kind === 'EXCHANGE_MATCH') {
+      base.fireMode = 'PER_EXCHANGE';
+      base.perExchangeLingerSeconds = 300;
+      base.filter = {};
+    }
     setForm({
       ...form,
       conditionKind: kind,
-      condition: { kind, scope: prev.scope } as FormState['condition'],
+      condition: base as FormState['condition'],
     });
   };
 
diff --git a/ui/src/pages/Alerts/RuleEditor/form-state.test.ts b/ui/src/pages/Alerts/RuleEditor/form-state.test.ts
index 40e68df8..ed1db316 100644
--- a/ui/src/pages/Alerts/RuleEditor/form-state.test.ts
+++ b/ui/src/pages/Alerts/RuleEditor/form-state.test.ts
@@ -47,4 +47,37 @@ describe('validateStep', () => {
     f.evaluationIntervalSeconds = 1;
     expect(validateStep('trigger', f).some((e) => /Evaluation interval/.test(e))).toBe(true);
   });
+
+  it('flags missing fireMode on EXCHANGE_MATCH condition step', () => {
+    const f = initialForm();
+    f.conditionKind = 'EXCHANGE_MATCH';
+    // Simulate the old bug: condition payload without a fireMode.
+    f.condition = { kind: 'EXCHANGE_MATCH', scope: {} } as typeof f.condition;
+    expect(validateStep('condition', f).some((e) => /Fire mode is required/.test(e))).toBe(true);
+  });
+
+  it('flags missing threshold/window on COUNT_IN_WINDOW', () => {
+    const f = initialForm();
+    f.conditionKind = 'EXCHANGE_MATCH';
+    f.condition = {
+      kind: 'EXCHANGE_MATCH',
+      scope: {},
+      fireMode: 'COUNT_IN_WINDOW',
+    } as unknown as typeof f.condition;
+    const errs = validateStep('condition', f);
+    expect(errs.some((e) => /Threshold is required/.test(e))).toBe(true);
+    expect(errs.some((e) => /Window/.test(e))).toBe(true);
+  });
+
+  it('passes when EXCHANGE_MATCH PER_EXCHANGE has linger seconds', () => {
+    const f = initialForm();
+    f.conditionKind = 'EXCHANGE_MATCH';
+    f.condition = {
+      kind: 'EXCHANGE_MATCH',
+      scope: {},
+      fireMode: 'PER_EXCHANGE',
+      perExchangeLingerSeconds: 300,
+    } as unknown as typeof f.condition;
+    expect(validateStep('condition', f)).toEqual([]);
+  });
 });
diff --git a/ui/src/pages/Alerts/RuleEditor/form-state.ts b/ui/src/pages/Alerts/RuleEditor/form-state.ts
index 3de5b9d5..120c70af 100644
--- a/ui/src/pages/Alerts/RuleEditor/form-state.ts
+++ b/ui/src/pages/Alerts/RuleEditor/form-state.ts
@@ -147,6 +147,19 @@ export function validateStep(step: WizardStep, f: FormState): string[] {
   }
   if (step === 'condition') {
     if (!f.conditionKind) errs.push('Condition kind is required.');
+    if (f.conditionKind === 'EXCHANGE_MATCH') {
+      const c = f.condition as Record<string, unknown>;
+      if (!c.fireMode) {
+        errs.push('Fire mode is required.');
+      } else if (c.fireMode === 'PER_EXCHANGE') {
+        if (c.perExchangeLingerSeconds == null) {
+          errs.push('Linger seconds is required for PER_EXCHANGE.');
+        }
+      } else if (c.fireMode === 'COUNT_IN_WINDOW') {
+        if (c.threshold == null) errs.push('Threshold is required for COUNT_IN_WINDOW.');
+        if (c.windowSeconds == null) errs.push('Window (seconds) is required for COUNT_IN_WINDOW.');
+      }
+    }
   }
   if (step === 'trigger') {
     if (f.evaluationIntervalSeconds < 5) errs.push('Evaluation interval must be \u2265 5 s.');