diff --git a/otk/userstring.hh b/otk/userstring.hh
index 601d54e4..c7c81d0c 100644
--- a/otk/userstring.hh
+++ b/otk/userstring.hh
@@ -9,6 +9,8 @@ extern "C" {
 #include <assert.h>
 }
 
+namespace otk {
+
 //! userstring is a std::string with an extra flag specifying if the string is
 //! UTF-8 encoded.
 class userstring : public std::string
@@ -101,4 +103,6 @@ public:
   }
 };
 
+}
+
 #endif // __userstring_hh