diff --git a/packages/@aws-cdk/cloudformation-diff/lib/diff/util.ts b/packages/@aws-cdk/cloudformation-diff/lib/diff/util.ts
index 1cbd4b1a111d7..b1e6146cf8afd 100644
--- a/packages/@aws-cdk/cloudformation-diff/lib/diff/util.ts
+++ b/packages/@aws-cdk/cloudformation-diff/lib/diff/util.ts
@@ -27,6 +27,13 @@ export function deepEqual(lvalue: any, rvalue: any): boolean {
       safeParseFloat(lvalue) === safeParseFloat(rvalue)) {
     return true;
   }
+  // GetStackTemplate flattens any codepoint greater than "\u7f" to "?". This
+  // is true even for codepoints in the supplemental planes which are
+  // represented in JS as surrogate pairs, all the way up to "\u{10ffff}".
+  if (typeof lvalue === 'string' && typeof rvalue === 'string' &&
+      lvalue === rvalue.replace(/[\u{80}-\u{10ffff}]/gu, '?')) {
+    return true;
+  }
   if (typeof lvalue !== typeof rvalue) { return false; }
   if (Array.isArray(lvalue) !== Array.isArray(rvalue)) { return false; }
   if (Array.isArray(lvalue) /* && Array.isArray(rvalue) */) {
diff --git a/packages/@aws-cdk/cloudformation-diff/test/deep-equal.test.ts b/packages/@aws-cdk/cloudformation-diff/test/deep-equal.test.ts
new file mode 100644
index 0000000000000..59df74fa37552
--- /dev/null
+++ b/packages/@aws-cdk/cloudformation-diff/test/deep-equal.test.ts
@@ -0,0 +1,11 @@
+import { deepEqual } from '../lib/diff/util';
+
+test('mangled strings', () => {
+  expect(deepEqual('foo', 'foo')).toBeTruthy();
+  expect(deepEqual('????', '文字化け')).toBeTruthy();
+  expect(deepEqual('?????', '🤦🏻‍♂️')).toBeTruthy();
+  expect(deepEqual('?', '\u{10ffff}')).toBeTruthy();
+  expect(deepEqual('\u007f', '\u007f')).toBeTruthy();
+  expect(deepEqual('?', '\u007f')).toBeFalsy();
+  expect(deepEqual('?', '\u0080')).toBeTruthy();
+});