diff --git a/src/DataTree.hh b/src/DataTree.hh
index 58b06aaccf1976bf5ee7938c0573b924a6639634..81f0223f8c9bf9a92d2c83171560ad84950a6a1c 100644
--- a/src/DataTree.hh
+++ b/src/DataTree.hh
@@ -146,7 +146,7 @@ public:
   {
   public:
     string name;
-    LocalVariableException(str name_arg) : name(name_arg) {}
+    LocalVariableException(string name_arg) : name(name_arg) {}
   };
 
   class DivisionByZeroException