diff --git a/include/json/value.h b/include/json/value.h
index 14c4129..229aa9e 100644
--- a/include/json/value.h
+++ b/include/json/value.h
@@ -518,7 +518,7 @@ private:
     LargestUInt uint_;
     double real_;
     bool bool_;
-    char* string_;
+    char* string_;  // actually ptr to unsigned, followed by str
     ObjectValues* map_;
   } value_;
   ValueType type_ : 8;
diff --git a/src/lib_json/json_value.cpp b/src/lib_json/json_value.cpp
index 3378e76..eae87db 100644
--- a/src/lib_json/json_value.cpp
+++ b/src/lib_json/json_value.cpp
@@ -100,6 +100,28 @@ static inline char* duplicateStringValue(const char* value,
   return newString;
 }
 
+/* Record the length as a prefix.
+ */
+static inline char* duplicatePrefixedStringValue(
+    const char* value,
+    unsigned int length = unknown)
+{
+  if (length == unknown)
+    length = (unsigned int)strlen(value);
+
+  // Avoid an integer overflow in the call to malloc below by limiting length
+  // to a sane value.
+  if (length >= (unsigned)Value::maxInt)
+    length = Value::maxInt - 1;
+
+  char* newString = static_cast<char*>(malloc(length + 1));
+  JSON_ASSERT_MESSAGE(newString != 0,
+                      "in Json::Value::duplicateStringValue(): "
+                      "Failed to allocate string value buffer");
+  memcpy(newString, value, length);
+  newString[length] = 0;
+  return newString;
+}
 /** Free the string duplicated by duplicateStringValue().
  */
 static inline void releaseStringValue(char* value) { free(value); }