diff --git a/src/parsing/scanner-character-streams.cc b/src/parsing/scanner-character-streams.cc
index 7ac7af74ab..052b6007ae 100644
--- a/src/parsing/scanner-character-streams.cc
+++ b/src/parsing/scanner-character-streams.cc
@@ -564,9 +564,11 @@ Utf16CharacterStream* ScannerStream::For(Isolate* isolate, Handle<String> data,
   if (data->IsSlicedString()) {
     SlicedString* string = SlicedString::cast(*data);
     start_offset = string->offset();
-    data = handle(string->parent(), string->GetIsolate());
+    String* parent = string->parent();
+    if (parent->IsThinString()) parent = ThinString::cast(parent)->actual();
+    data = handle(parent, isolate);
   } else {
-    data = String::Flatten(data->GetIsolate(), data);
+    data = String::Flatten(isolate, data);
   }
   if (data->IsExternalOneByteString()) {
     return new BufferedCharacterStream<uint8_t, ExternalStringStream>(
diff --git a/test/mjsunit/regress/regress-crbug-862538.js b/test/mjsunit/regress/regress-crbug-862538.js
new file mode 100644
index 0000000000..f5da2eecbe
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-862538.js
@@ -0,0 +1,13 @@
+// Copyright 2018 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var uvwxyzundefined;
+
+function __f_5778(__v_29973) {
+  var __v_29975 = __v_29973 + undefined;
+  var __v_29976 = __v_29975.substring( 20);
+  ({})[__v_29975];
+  return eval(__v_29976);
+}
+__f_5778("abcdefghijklmnopqrstuvwxyz");