diff --git a/src/support/convert.C b/src/support/convert.C
index bd8dc2ec17..a3014fe418 100644
--- a/src/support/convert.C
+++ b/src/support/convert.C
@@ -82,6 +82,13 @@ string convert<string>(unsigned long ul)
 }
 
 
+template<>
+docstring convert<docstring>(unsigned long ul)
+{
+	return lyx::from_ascii(lexical_cast<string>(ul));
+}
+
+
 template<>
 string convert<string>(long l)
 {