diff --git a/mfbt/HashFunctions.h b/mfbt/HashFunctions.h
index 6d0d24e7b1c8..b228955ce5bb 100644
--- a/mfbt/HashFunctions.h
+++ b/mfbt/HashFunctions.h
@@ -48,6 +48,7 @@
 
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
+#include "mozilla/Char16.h"
 #include "mozilla/Types.h"
 
 #include <stdint.h>
@@ -326,6 +327,22 @@ HashString(const uint16_t* str, size_t length)
   return detail::HashKnownLength(str, length);
 }
 
+#ifdef MOZ_CHAR16_IS_NOT_WCHAR
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashString(const char16_t* str)
+{
+  return detail::HashUntilZero(str);
+}
+
+MOZ_WARN_UNUSED_RESULT
+inline uint32_t
+HashString(const char16_t* str, size_t length)
+{
+  return detail::HashKnownLength(str, length);
+}
+#endif
+
 /*
  * On Windows, wchar_t (PRUnichar) is not the same as uint16_t, even though it's
  * the same width!