diff --git a/pyerrors/correlators.py b/pyerrors/correlators.py
index ea767ec5..aaf32ba6 100644
--- a/pyerrors/correlators.py
+++ b/pyerrors/correlators.py
@@ -255,6 +255,7 @@ class Corr:
         return True
 
     def trace(self):
+        """Calculates the per-timeslice trace of a correlator matrix."""
         if self.N == 1:
             raise TypeError("Only works for correlator matrices.")
         newcontent = []