diff --git a/cnumber.hpp b/cnumber.hpp
index 51a2f3e..f8cd7d8 100644
--- a/cnumber.hpp
+++ b/cnumber.hpp
@@ -76,6 +76,9 @@ public:
       }
       os << 'i';
     }
+    if (z.r == 0 && z.i == 0) {
+      os << '0';
+    }
     return os;
   }
   void operator=(const cnumber &z) {