diff --git a/packages/@apphosting/adapter-nextjs/src/utils.spec.ts b/packages/@apphosting/adapter-nextjs/src/utils.spec.ts
index bea48526f..03ebc469b 100644
--- a/packages/@apphosting/adapter-nextjs/src/utils.spec.ts
+++ b/packages/@apphosting/adapter-nextjs/src/utils.spec.ts
@@ -57,6 +57,21 @@ describe("block vulnerable nextjs versions", () => {
     assert.doesNotThrow(() => {
       checkNextJSVersion("16.0.7");
     });
+
+    assert.doesNotThrow(() => {
+      checkNextJSVersion("16.3.0-preview");
+    });
+
+    // A prerelease of an unpatched minor must NOT slip past the bounded ranges:
+    // 16.1.0-canary.2 sorts below 16.1.0 (the first patched release) and
+    // 15.1.0-canary.2 below the patched 15.1.9, so both stay blocked.
+    assert.throws(() => {
+      checkNextJSVersion("16.1.0-canary.2");
+    });
+
+    assert.throws(() => {
+      checkNextJSVersion("15.1.0-canary.2");
+    });
   });
 });
 
diff --git a/packages/@apphosting/adapter-nextjs/src/utils.ts b/packages/@apphosting/adapter-nextjs/src/utils.ts
index 5ea568d7e..3819a0b8f 100644
--- a/packages/@apphosting/adapter-nextjs/src/utils.ts
+++ b/packages/@apphosting/adapter-nextjs/src/utils.ts
@@ -23,11 +23,25 @@ export const { satisfies } = semVer;
 const SAFE_NEXTJS_VERSIONS =
   ">=16.1.0 || ~16.0.7 || ~v15.5.7 || ~v15.4.8 || ~v15.3.6 || ~v15.2.6 || ~v15.1.9 || ~v15.0.5 || <14.3.0-canary.77";
 
+// The latest line is patched from 16.1.0 onward, so any prerelease of a version
+// >= 16.1.0 (e.g. the `next@preview` tag, which resolves to "16.3.0-preview") is
+// safe. We only enable includePrerelease for this open-ended range. Applying it
+// to the whole SAFE_NEXTJS_VERSIONS range would loosen the bounded `~`/`<`
+// comparators of older lines, potentially letting a prerelease of an unpatched
+// minor slip through.
+const SAFE_NEXTJS_PRERELEASE_RANGE = ">=16.1.0";
+
 export function checkNextJSVersion(version: string | undefined) {
   if (!version) {
     return;
   }
-  if (!satisfies(version, SAFE_NEXTJS_VERSIONS)) {
+  // Default (strict) matching covers stable versions and the canary boundary,
+  // then scoped includePrerelease admits only prereleases of the patched >=16.1.0
+  // line. A version is vulnerable only if it satisfies neither.
+  if (
+    !satisfies(version, SAFE_NEXTJS_VERSIONS) &&
+    !satisfies(version, SAFE_NEXTJS_PRERELEASE_RANGE, { includePrerelease: true })
+  ) {
     throw new Error(
       `CVE-2025-55182: Vulnerable Next version ${version} detected. Deployment blocked. Update your app's dependencies to a patched Next.js version and redeploy: https://nextjs.org/blog/CVE-2025-66478#fixed-versions`,
     );