diff --git a/source/lib-intro.tex b/source/lib-intro.tex
index c633910187..b78c4f80eb 100644
--- a/source/lib-intro.tex
+++ b/source/lib-intro.tex
@@ -564,7 +564,7 @@
       }
     };
 
-  template<class T, class U=T>
+  template<class T, class U = T>
   using @\placeholdernc{synth-three-way-result}@ =                  // \expos
     decltype(@\placeholdernc{synth-three-way}@(declval<T&>(), declval<U&>()));
 }