diff --git a/packages/cli/src/lib/db/auth.ts b/packages/cli/src/lib/db/auth.ts
index da16edf19..1e391a80e 100644
--- a/packages/cli/src/lib/db/auth.ts
+++ b/packages/cli/src/lib/db/auth.ts
@@ -74,6 +74,26 @@ export const REFRESH_THRESHOLD = 0.1;
 /** Default token lifetime (1 hour) for tokens without issuedAt */
 export const DEFAULT_TOKEN_LIFETIME_MS = 3600 * 1000;
 
+/**
+ * Fraction of a token's lifetime that remains at `now`.
+ *
+ * Uses {@link DEFAULT_TOKEN_LIFETIME_MS} when `issuedAt` is missing or not
+ * before `expiresAt`. A corrupt row with `issued_at >= expires_at` would
+ * otherwise divide by zero or flip the sign, and an `Infinity` ratio skips
+ * proactive refresh.
+ */
+export function getRemainingLifetimeRatio(
+  expiresAt: number,
+  issuedAt: number | null | undefined,
+  now: number,
+): number {
+  const storedLifetime =
+    issuedAt === null || issuedAt === undefined ? 0 : expiresAt - issuedAt;
+  const totalLifetime =
+    storedLifetime > 0 ? storedLifetime : DEFAULT_TOKEN_LIFETIME_MS;
+  return (expiresAt - now) / totalLifetime;
+}
+
 /**
  * The active account row. `host` is NULL only for rows migrated from the
  * pre-v16 `auth` table; `migrateNullHost` backfills it on access.
@@ -1679,10 +1699,12 @@ export async function refreshToken(
     return { ...baseResult, token: row.token, refreshed: false };
   }
 
-  const issuedAt = row.issued_at ?? expiresAt - DEFAULT_TOKEN_LIFETIME_MS;
-  const totalLifetime = expiresAt - issuedAt;
   const remainingLifetime = expiresAt - now;
-  const remainingRatio = remainingLifetime / totalLifetime;
+  const remainingRatio = getRemainingLifetimeRatio(
+    expiresAt,
+    row.issued_at,
+    now,
+  );
   const expiresIn = Math.max(0, Math.floor(remainingLifetime / 1000));
 
   if (!force && remainingRatio > REFRESH_THRESHOLD && now < expiresAt) {
diff --git a/packages/cli/src/lib/sentry-client.ts b/packages/cli/src/lib/sentry-client.ts
index ac25222c3..fae7b82ae 100644
--- a/packages/cli/src/lib/sentry-client.ts
+++ b/packages/cli/src/lib/sentry-client.ts
@@ -32,8 +32,8 @@ import {
 import { applyCustomHeaders } from "./custom-headers.js";
 import {
   type CredentialContext,
-  DEFAULT_TOKEN_LIFETIME_MS,
   getCredentialContext,
+  getRemainingLifetimeRatio,
   REFRESH_THRESHOLD,
   refreshToken,
 } from "./db/auth.js";
@@ -631,19 +631,14 @@ async function fetchWithRetry({
   validatedRedirects,
   responseBodyMode,
 }: RetryContext): Promise<Response> {
-  const issuedAt =
-    credential.issuedAt ??
-    (credential.expiresAt
-      ? credential.expiresAt - DEFAULT_TOKEN_LIFETIME_MS
-      : undefined);
   const shouldRefresh = Boolean(
     credential.refreshable &&
     credential.expiresAt &&
-    (Date.now() >= credential.expiresAt ||
-      (issuedAt &&
-        (credential.expiresAt - Date.now()) /
-          (credential.expiresAt - issuedAt) <=
-          REFRESH_THRESHOLD)),
+    getRemainingLifetimeRatio(
+      credential.expiresAt,
+      credential.issuedAt,
+      Date.now(),
+    ) <= REFRESH_THRESHOLD,
   );
   const refreshed = shouldRefresh
     ? await refreshToken({ expectedCredential: credential })
diff --git a/packages/cli/test/lib/db/auth.test.ts b/packages/cli/test/lib/db/auth.test.ts
index 392be4283..6fb5b3a03 100644
--- a/packages/cli/test/lib/db/auth.test.ts
+++ b/packages/cli/test/lib/db/auth.test.ts
@@ -11,14 +11,17 @@ import { describe, expect, test } from "vitest";
 import {
   ANON_IDENTITY,
   clearAuth,
+  DEFAULT_TOKEN_LIFETIME_MS,
   getActiveEnvVarName,
   getAuthConfig,
   getAuthToken,
   getIdentityFingerprint,
   getRawEnvToken,
+  getRemainingLifetimeRatio,
   hasStoredAuthCredentials,
   isAuthenticated,
   isEnvTokenActive,
+  REFRESH_THRESHOLD,
   refreshToken,
   resetAuthTokenCache,
   resetHasStoredCredsCache,
@@ -437,6 +440,19 @@ describe("refreshToken row-read memoization", () => {
   });
 });
 
+describe("refreshToken: corrupt issued_at", () => {
+  test("proactively refreshes when issued_at equals expires_at", async () => {
+    // 2 minutes left is under 10% of the default 1h lifetime. A zero stored
+    // lifetime used to read as an Infinity ratio and skip the refresh path.
+    setAuthToken("corrupt_access", 120);
+    getDatabase().query("UPDATE accounts SET issued_at = expires_at").run();
+    process.env.SENTRY_AUTH_TOKEN = "env_token";
+
+    const result = await refreshToken();
+    expect(result.token).toBe("env_token");
+  });
+});
+
 describe("hasStoredAuthCredentials memoization", () => {
   test("returns false and caches when no stored token", () => {
     expect(hasStoredAuthCredentials()).toBe(false);
@@ -479,3 +495,41 @@ describe("hasStoredAuthCredentials memoization", () => {
     expect(hasStoredAuthCredentials()).toBe(true);
   });
 });
+
+describe("getRemainingLifetimeRatio", () => {
+  const now = 1_000_000_000;
+
+  test("uses the stored lifetime when issuedAt precedes expiresAt", () => {
+    expect(getRemainingLifetimeRatio(now + 500, now - 500, now)).toBe(0.5);
+  });
+
+  test("falls back to the default lifetime when issuedAt is missing", () => {
+    const expiresAt = now + DEFAULT_TOKEN_LIFETIME_MS / 4;
+    expect(getRemainingLifetimeRatio(expiresAt, null, now)).toBe(0.25);
+    expect(getRemainingLifetimeRatio(expiresAt, undefined, now)).toBe(0.25);
+  });
+
+  test.each([
+    ["issued_at equals expires_at", 0],
+    ["issued_at after expires_at", 1000],
+  ])(
+    "falls back to the default lifetime when %s",
+    (_label, issuedAfterExpiry) => {
+      // 5% of the default lifetime remains, so a sane lifetime must trigger
+      // proactive refresh instead of reading as Infinity or a huge ratio.
+      const expiresAt = now + DEFAULT_TOKEN_LIFETIME_MS * 0.05;
+      const ratio = getRemainingLifetimeRatio(
+        expiresAt,
+        expiresAt + issuedAfterExpiry,
+        now,
+      );
+      expect(ratio).toBeCloseTo(0.05);
+      expect(ratio).toBeLessThanOrEqual(REFRESH_THRESHOLD);
+    },
+  );
+
+  test("is non-positive once the token has expired", () => {
+    expect(getRemainingLifetimeRatio(now, now, now)).toBe(0);
+    expect(getRemainingLifetimeRatio(now - 1, now - 1, now)).toBeLessThan(0);
+  });
+});