diff --git a/Doc/library/csv.rst b/Doc/library/csv.rst
index 87c2d4702e7408..323e209e889fd1 100644
--- a/Doc/library/csv.rst
+++ b/Doc/library/csv.rst
@@ -312,6 +312,11 @@ The :mod:`!csv` module defines the following classes:
       is given, it is interpreted as a string containing possible valid
       delimiter characters.
 
+      If several combinations fit the sample equally well ---
+      for example if both ``','`` and ``';'`` split every row consistently ---
+      the delimiters ``','``, ``'\t'``, ``';'``, ``' '`` and ``':'``
+      are preferred, in this order,
+      no matter how many times each of them occurs.
 
    .. method:: has_header(sample)
 
diff --git a/Lib/csv.py b/Lib/csv.py
index 6cae34c705777d..90dbf87f7363bb 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -241,6 +241,10 @@ def __init__(self):
     def sniff(self, sample, delimiters=None):
         """
         Returns a dialect (or None) corresponding to the sample
+
+        If several combinations fit the sample equally well, the
+        delimiters listed in the preferred attribute are preferred, in
+        that order, no matter how many times each of them occurs.
         """
 
         quotechar, doublequote, delimiter, skipinitialspace = \