diff --git a/CHANGELOG.md b/CHANGELOG.md
index cbb487f259ca1836ae23519ed66cb03566827084..fe5888aa30004bb363b680d7f8ac1b4d036eade0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 # v2.26.7
 
-* _TBA_
+* fixed `__str__` method of `CustomException`
 
 # v2.26.6
 
diff --git a/satella/exceptions.py b/satella/exceptions.py
index 9ac1a0ed29af1b90dcba4b1ed22dbe9735a30b5e..73c4ab62328f8f24f588bac07a234b4b12663e2e 100644
--- a/satella/exceptions.py
+++ b/satella/exceptions.py
@@ -29,7 +29,7 @@ class CustomException(Exception):
         a = '%s(%s' % (self.__class__.__qualname__.split('.')[-1], ', '.join(map(repr, self.args)))
         try:
             if self.kwargs:
-                a += ', ' + ', '.join(map(lambda k, v: '%s=%s' % (k, repr(v)), self.kwargs.items()))
+                a += ', ' + ', '.join('%s=%s' % (k, repr(v)) for k, v in self.kwargs.items())
         except AttributeError:
             pass
         a += ')'
@@ -42,8 +42,7 @@ class CustomException(Exception):
                          ', '.join(map(repr, self.args)))
         try:
             if self.kwargs:
-                a += ', ' + (', '.join(map(lambda kv: '%s=%s' % (kv[0], repr(kv[1])),
-                                           self.kwargs.items())))
+                a += ', ' + ', '.join('%s=%s' % (k, repr(v)) for k, v in self.kwargs.items())
         except AttributeError:
             pass
         a += ')'