diff --git a/turtle/detail/matcher_base.hpp b/turtle/detail/matcher_base.hpp
index 7ed24fc..77cdf49 100644
--- a/turtle/detail/matcher_base.hpp
+++ b/turtle/detail/matcher_base.hpp
@@ -24,7 +24,8 @@ namespace detail
 
         virtual bool operator()( Actual ) = 0;
 
-        friend std::ostream& operator<<( std::ostream& s, const matcher_base& c )
+        friend std::ostream& operator<<(
+            std::ostream& s, const matcher_base& c )
         {
             c.serialize( s );
             return s;