diff --git a/packages/account-core/src/index.test.ts b/packages/account-core/src/index.test.ts
index c00a8e3..6f67303 100644
--- a/packages/account-core/src/index.test.ts
+++ b/packages/account-core/src/index.test.ts
@@ -24,6 +24,13 @@ describe("account-core", () => {
     expect(riskBandForScore(score)).toBe("high");
   });
 
+  it.each([Number.NaN, Number.POSITIVE_INFINITY, Number.NEGATIVE_INFINITY])(
+    "classifies a non-finite risk score of %s as critical",
+    (riskScore) => {
+      expect(riskBandForScore(riskScore)).toBe("critical");
+    }
+  );
+
   it("requires approval for gated actions with matching grants", () => {
     const result = evaluateAccountPolicy({
       action: "email:send",
@@ -41,6 +48,31 @@ describe("account-core", () => {
     expect(result.decision).toBe("approval_required");
   });
 
+  it.each([Number.NaN, Number.POSITIVE_INFINITY, Number.NEGATIVE_INFINITY])(
+    "fails closed for a non-finite risk score of %s",
+    (riskScore) => {
+      const result = evaluateAccountPolicy({
+        action: "social:profile:read",
+        riskScore,
+        principal: { type: "agent", id: "profile-agent" },
+        grant: {
+          id: "grant_non_finite",
+          accountId: "account_1",
+          principal: { type: "agent", id: "profile-agent" },
+          permissions: ["social:profile:read"],
+          policy: [],
+          createdAt: new Date(0).toISOString()
+        }
+      });
+
+      expect(result).toMatchObject({
+        decision: "deny",
+        riskScore: 1,
+        reason: "critical risk requires admin override"
+      });
+    }
+  );
+
   it("redacts secret-like audit previews", () => {
     const event = createAccountAuditEvent({
       provider: "gmail",
diff --git a/packages/account-core/src/policy.ts b/packages/account-core/src/policy.ts
index b80ed25..d91cd4b 100644
--- a/packages/account-core/src/policy.ts
+++ b/packages/account-core/src/policy.ts
@@ -14,6 +14,9 @@ const WRITE_ACTIONS = new Set([
 ]);
 
 export function riskBandForScore(score: number): LogicSrcRiskBand {
+  if (!Number.isFinite(score)) {
+    return "critical";
+  }
   if (score >= 0.75) {
     return "critical";
   }
@@ -51,7 +54,8 @@ export function scoreAccountActionRisk(input: {
 }
 
 export function evaluateAccountPolicy(input: LogicSrcPolicyEvaluationInput): LogicSrcPolicyEvaluationResult {
-  const riskScore = Math.min(1, Math.max(0, input.riskScore ?? scoreAccountActionRisk({ action: input.action })));
+  const requestedRiskScore = input.riskScore ?? scoreAccountActionRisk({ action: input.action });
+  const riskScore = Number.isFinite(requestedRiskScore) ? Math.min(1, Math.max(0, requestedRiskScore)) : 1;
   const grantActive = input.grant && !input.grant.revokedAt && (!input.grant.expiresAt || Date.parse(input.grant.expiresAt) > Date.now());
   const hasPermission = Boolean(grantActive && input.grant?.permissions.includes(input.action));