diff --git a/pyerrors/pyerrors.py b/pyerrors/pyerrors.py
index a807871f..82bf7154 100644
--- a/pyerrors/pyerrors.py
+++ b/pyerrors/pyerrors.py
@@ -638,8 +638,10 @@ class CObs:
         self.imag = imag
 
     def gamma_method(self, **kwargs):
-        self.real.gamma_method(**kwargs)
-        self.imag.gamma_method(**kwargs)
+        if isinstance(self.real, Obs):
+            self.real.gamma_method(**kwargs)
+        if isinstance(self.imag, Obs):
+            self.imag.gamma_method(**kwargs)
 
     def __add__(self, other):
         if hasattr(other, 'real') and hasattr(other, 'imag'):