diff --git a/developer/src/kmc-kmn/src/compiler/compiler.ts b/developer/src/kmc-kmn/src/compiler/compiler.ts
index 33d1b545f5..c3c3bb3256 100644
--- a/developer/src/kmc-kmn/src/compiler/compiler.ts
+++ b/developer/src/kmc-kmn/src/compiler/compiler.ts
@@ -421,6 +421,12 @@ export class KmnCompiler implements UnicodeSetParser {
     return Module.kmcmp_testSentry();
   }
 
+  /** convert `\u{1234}` to `\u1234` */
+  public static fixNewPattern(pattern: string) : string {
+    return pattern.replaceAll(/\\u\{([0-9a-fA-F]{4})\}/g, `\\u$1`);
+    // TODO-LDML: other lengths! #9515
+  }
+
   /**
    *
    * @param pattern UnicodeSet pattern such as `[a-z]`
@@ -435,6 +441,8 @@ export class KmnCompiler implements UnicodeSetParser {
 
     // TODO-LDML: Catch OOM
     const buf = this.wasmExports.malloc(rangeCount * 2 * Module.HEAPU32.BYTES_PER_ELEMENT);
+    // fix \u1234 pattern format
+    pattern = KmnCompiler.fixNewPattern(pattern);
     /** If <= 0: return code. If positive: range count */
     const rc = Module.kmcmp_parseUnicodeSet(pattern, buf, rangeCount * 2);
     if (rc >= 0) {
@@ -459,6 +467,8 @@ export class KmnCompiler implements UnicodeSetParser {
       /* c8 ignore next 2 */
       return null;
     }
+    // fix \u1234 pattern format
+    pattern = KmnCompiler.fixNewPattern(pattern);
     // call with rangeCount = 0 to invoke in 'preflight' mode.
     const rc = Module.kmcmp_parseUnicodeSet(pattern, 0, 0);
     if (rc >= 0) {
diff --git a/developer/src/kmc-kmn/test/test-wasm-uset.ts b/developer/src/kmc-kmn/test/test-wasm-uset.ts
index a924f9fe05..3d9c4e0139 100644
--- a/developer/src/kmc-kmn/test/test-wasm-uset.ts
+++ b/developer/src/kmc-kmn/test/test-wasm-uset.ts
@@ -6,6 +6,18 @@ import { CompilerMessages } from '../src/compiler/messages.js';
 import { compilerErrorFormatCode } from '@keymanapp/common-types';
 
 describe('Compiler UnicodeSet function', function() {
+  it('should fixup \\u1234 format escapes', function() {
+    assert.equal(KmnCompiler.fixNewPattern(`\\u{1234}`), `\\u1234`);
+    assert.equal(KmnCompiler.fixNewPattern(`\\u1234`), `\\u1234`);
+    assert.equal(KmnCompiler.fixNewPattern(`[\\u{1234}-\\u{5678}]`), `[\\u1234-\\u5678]`);
+    assert.equal(KmnCompiler.fixNewPattern(`something else`), `something else`);
+  });
+
+  it.skip('should fixup more creative \\u format escapes', function() {
+    assert.equal(KmnCompiler.fixNewPattern(`\\u{22}`), `\\u0022`); // "
+    assert.equal(KmnCompiler.fixNewPattern(`\\u{1F640}`), `\\uD83D\\uDE40`);  // TODO-LDM #9515: or something, 🙀
+  });
+
   it('should start', async function() {
     const compiler = new KmnCompiler();
     const callbacks = new TestCompilerCallbacks();