diff --git a/eo/src/EO.h b/eo/src/EO.h
index 81668b897..7b1b503f2 100644
--- a/eo/src/EO.h
+++ b/eo/src/EO.h
@@ -108,7 +108,7 @@ public:
    */
   virtual void readFrom(istream& _is) { 
     _is >> repFitness;
-    if (is)
+    if (_is)
       invalidFitness = false;
     else
       throw runtime_error("EO(istream&): can't read valid eo from istream");