diff --git a/src/converter/builtin_converters.cpp b/src/converter/builtin_converters.cpp
index 2ce1fe9f..e1dead43 100644
--- a/src/converter/builtin_converters.cpp
+++ b/src/converter/builtin_converters.cpp
@@ -304,13 +304,16 @@ namespace
       static std::wstring extract(PyObject* intermediate)
       {
           std::wstring result(::PyObject_Length(intermediate), L' ');
-          int err = PyUnicode_AsWideChar(
-              (PyUnicodeObject *)intermediate
-            , result.size() ? &result[0] : 0
-            , result.size());
+          if (!result.empty())
+          {
+              int err = PyUnicode_AsWideChar(
+                  (PyUnicodeObject *)intermediate
+                , &result[0]
+                , result.size());
 
-          if (err == -1)
-              throw_error_already_set();
+              if (err == -1)
+                  throw_error_already_set();
+          }
           return result;
       }
   };