diff --git a/pyerrors/obs.py b/pyerrors/obs.py
index c1fcc8ca..38faa276 100644
--- a/pyerrors/obs.py
+++ b/pyerrors/obs.py
@@ -74,8 +74,10 @@ class Obs:
             if idl is not None:
                 if len(idl) != len(names):
                     raise Exception('Length of idl incompatible with samples and names.')
-            if len(names) != len(set(names)):
-                raise Exception('names are not unique.')
+            name_length = len(names)
+            if name_length > 1:
+                if name_length != len(set(names)):
+                    raise Exception('names are not unique.')
             if not all(isinstance(x, str) for x in names):
                 raise TypeError('All names have to be strings.')
             if min(len(x) for x in samples) <= 4: