diff --git a/packages/string_tokenizer/lib/string_tokenizer.dart b/packages/string_tokenizer/lib/string_tokenizer.dart
index 76c3f937..ad97e9e7 100644
--- a/packages/string_tokenizer/lib/string_tokenizer.dart
+++ b/packages/string_tokenizer/lib/string_tokenizer.dart
@@ -51,11 +51,13 @@ List<String> tokenize(
   range.ref.location = 0;
   range.ref.length = string.length;
 
+  final utf8 = string.toNativeUtf8();
   final cfString = _bindings.CFStringCreateWithCString(
     nullptr,
-    string.toNativeUtf8().cast(),
+    utf8.cast(),
     binding.CFStringBuiltInEncodings.kCFStringEncodingUTF8.value,
   );
+  malloc.free(utf8);
 
   int optionsInt = 0;
   for (final option in options) {