diff --git a/src/utils.ts b/src/utils.ts
index 7e8d906..88d7f8d 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -132,6 +132,17 @@ export function toBytes(data: Input): Uint8Array {
   return data;
 }
 
+/**
+ * Checks if two U8A use same underlying buffer and overlaps (will corrupt and break if input and output same)
+ */
+export function overlapBytes(a: Uint8Array, b: Uint8Array): boolean {
+  return (
+    a.buffer === b.buffer && // probably will fail with some obscure proxies, but this is best we can do
+    a.byteOffset < b.byteOffset + b.byteLength && // a starts before b end
+    b.byteOffset < a.byteOffset + a.byteLength // b starts before a end
+  );
+}
+
 /**
  * Copies several Uint8Arrays into one.
  */
@@ -237,6 +248,14 @@ export const wrapCipher = <C extends CipherCons<any>, P extends CipherParams>(
     }
 
     const cipher = constructor(key, ...args);
+    const checkOutput = (fnLength: number, data: Uint8Array, output?: Uint8Array) => {
+      if (output !== undefined) {
+        if (fnLength !== 2) throw new Error('cipher output not supported');
+        abytes(output);
+        if (overlapBytes(data, output))
+          throw new Error('input and output use same buffer and overlap');
+      }
+    };
 
     // Create wrapped cipher with validation and single-use encryption
     let called = false;
@@ -245,10 +264,12 @@ export const wrapCipher = <C extends CipherCons<any>, P extends CipherParams>(
         if (called) throw new Error('cannot encrypt() twice with same key + nonce');
         called = true;
         abytes(data);
+        checkOutput(cipher.encrypt.length, data, output);
         return (cipher as CipherWithOutput).encrypt(data, output);
       },
       decrypt(data: Uint8Array, output?: Uint8Array) {
         abytes(data);
+        checkOutput(cipher.decrypt.length, data, output);
         if (tagl && data.length < tagl)
           throw new Error('invalid ciphertext length: smaller than tagLength=' + tagl);
         return (cipher as CipherWithOutput).decrypt(data, output);
@@ -273,11 +294,9 @@ export type XorStream = (
 export function getOutput(expectedLength: number, out?: Uint8Array, onlyAligned = true) {
   if (out === undefined) return new Uint8Array(expectedLength);
   if (out.length !== expectedLength)
-    throw new Error(
-      'invalid output length, expected at least ' + expectedLength + ', got: ' + out.length
-    );
+    throw new Error('invalid output length, expected ' + expectedLength + ', got: ' + out.length);
   if (onlyAligned && !isAligned32(out)) throw new Error('invalid output, must be aligned');
-  return out.subarray(0, expectedLength).fill(0);
+  return out.fill(0);
 }
 
 // Polyfill for Safari 14
diff --git a/test/basic.test.js b/test/basic.test.js
index 72a73a4..c9368c7 100644
--- a/test/basic.test.js
+++ b/test/basic.test.js
@@ -133,6 +133,78 @@ describe('Basic', () => {
         }
       });
     }
+    should(`${k} (re-use)`, () => {
+      const { fn, keyLen } = opts;
+      const msg = new Uint8Array(2 * opts.fn.blockSize).fill(12);
+      const key = randomBytes(keyLen);
+      const nonce = randomBytes(fn.nonceLength);
+      const AAD = randomBytes(64);
+      let cipher = fn(key, nonce, AAD);
+      // Not supported!
+      if (k.startsWith('micro')) return;
+      if (k.startsWith('gcm')) return;
+      if (k.startsWith('siv')) return;
+      if (k.startsWith('aeskw')) return;
+      // Wrapper changes length :(
+      if (cipher.encrypt.length === 2) {
+        // Tmp buffer
+        let outLen = msg.length;
+        if (fn.tagLength) outLen += fn.tagLength;
+        if (k === 'xsalsa20poly1305') outLen += 16;
+        if (k.includes('cbc') || k.includes('ecb')) outLen += 16;
+        // Expected result
+        cipher = fn(key, nonce, AAD);
+        const exp = cipher.encrypt(msg);
+        const out = new Uint8Array(outLen);
+        // First pass
+        cipher = fn(key, nonce, AAD);
+        const res = cipher.encrypt(msg, out);
+        deepStrictEqual(res, exp);
+        // check if res is output
+        deepStrictEqual(res, out.subarray(res.byteOffset, res.byteOffset + res.length));
+        deepStrictEqual(res.buffer, out.buffer); // make sure that underlying array buffer is same
+        // Second pass
+        out.fill(42);
+        cipher = fn(key, nonce, AAD);
+        const res2 = cipher.encrypt(msg, out);
+        deepStrictEqual(res2, exp);
+        deepStrictEqual(res2, out.subarray(res2.byteOffset, res2.byteOffset + res2.length));
+        deepStrictEqual(res2.buffer, out.buffer); // make sure that underlying array buffer is same
+        // Throws on same buffer:
+        cipher = fn(key, nonce, AAD);
+        out.set(msg);
+        const msg2 = out.subarray(0, msg.length);
+        throws(() => cipher.encrypt(msg2, out));
+      }
+      if (cipher.decrypt.length === 2) {
+        // Expected result
+        cipher = fn(key, nonce, AAD);
+        const input = cipher.encrypt(msg);
+        // Tmp buffer
+        let outLen = msg.length;
+        if (k.endsWith('xsalsa20poly1305')) outLen += 32 + 16;
+        if (k.includes('cbc') || k.includes('ecb')) outLen += 16;
+        const out = new Uint8Array(outLen);
+        // First pass
+        const res = cipher.decrypt(input, out);
+        deepStrictEqual(res, msg);
+        deepStrictEqual(res, out.subarray(res.byteOffset, res.byteOffset + res.length));
+        deepStrictEqual(res.buffer, out.buffer); // make sure that underlying array buffer is same
+        // Second pass
+        out.fill(42);
+        const res2 = cipher.decrypt(input, out);
+        deepStrictEqual(res2, msg);
+        deepStrictEqual(res2, out.subarray(res2.byteOffset, res2.byteOffset + res2.length));
+        deepStrictEqual(res2.buffer, out.buffer); // make sure that underlying array buffer is same
+        // Throws on same buffer:
+        const tmp = new Uint8Array(Math.max(out.length, input.length));
+        tmp.set(input);
+        const out2 = tmp.subarray(0, out.length);
+        const input2 = tmp.subarray(0, input.length);
+        throws(() => cipher.decrypt(input2, out2));
+      }
+    });
+    // Human tests ^, AI abomination v
 
     should('unaligned', () => {
       if (!['xsalsa20poly1305', 'xchacha20poly1305', 'chacha20poly1305'].includes(k)) return;
diff --git a/test/utils.test.js b/test/utils.test.js
index afad541..1ce83f1 100644
--- a/test/utils.test.js
+++ b/test/utils.test.js
@@ -2,7 +2,7 @@ const { deepStrictEqual, throws } = require('assert');
 const fc = require('fast-check');
 const { describe, should } = require('micro-should');
 const { TYPE_TEST, unalign } = require('./utils.js');
-const { bytesToHex, concatBytes, hexToBytes } = require('../utils.js');
+const { bytesToHex, concatBytes, hexToBytes, overlapBytes } = require('../utils.js');
 
 describe('utils', () => {
   const staticHexVectors = [
@@ -57,6 +57,41 @@ describe('utils', () => {
       })
     )
   );
+  should('sameBytes', () => {
+    // Basic
+    const buffer = new ArrayBuffer(20);
+    const a = new Uint8Array(buffer, 0, 10); // Bytes 0-9
+    const b = new Uint8Array(buffer, 5, 10); // Bytes 5-14
+    const c = new Uint8Array(buffer, 10, 10); // Bytes 10-19
+    const d = new Uint8Array(new ArrayBuffer(20), 0, 10); // Different buffer
+    deepStrictEqual(overlapBytes(a, b), true);
+    deepStrictEqual(overlapBytes(a, c), false);
+    deepStrictEqual(overlapBytes(b, c), true);
+    deepStrictEqual(overlapBytes(a, d), false);
+    // Scan
+    const res = [];
+    const main = new Uint8Array(8 + 4); // 2byte + first + 2byte
+    const first = main.subarray(2).subarray(0, 8);
+    for (let i = 0; i < main.length; i++) {
+      const second = main.subarray(i).subarray(0, 1); // one byte window
+      deepStrictEqual(second, new Uint8Array(1));
+      res.push(overlapBytes(first, second));
+    }
+    deepStrictEqual(res, [
+      false,
+      false,
+      true,
+      true,
+      true,
+      true,
+      true,
+      true,
+      true,
+      true,
+      false,
+      false,
+    ]);
+  });
 });
 
 describe('utils etc', () => {