new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/basic/bug1091757.js
@@ -0,0 +1,11 @@
+try {
+    (function() {
+	let a = 3;
+	let XY = XY;
+	return function() { return a; };
+    })();
+    assertEq(0, 1);
+} catch(e) {
+    assertEq(e instanceof ReferenceError, true);
+    assertEq(e.message.contains("XY"), true);
+}

--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -4066,17 +4066,17 @@ js::ReportUninitializedLexical(JSContext
 {
     RootedPropertyName name(cx);
 
     if (JSOp(*pc) == JSOP_CHECKLEXICAL) {
         uint32_t slot = GET_LOCALNO(pc);
 
         // First search for a name among body-level lets.
         for (BindingIter bi(script); bi; bi++) {
-            if (bi->kind() != Binding::ARGUMENT && bi.frameIndex() == slot) {
+            if (bi->kind() != Binding::ARGUMENT && !bi->aliased() && bi.frameIndex() == slot) {
                 name = bi->name();
                 break;
             }
         }
 
         // Failing that, it must be a block-local let.
         if (!name) {
             // Skip to the right scope.