diff --git a/scipost_django/common/converters.py b/scipost_django/common/converters.py
index 5dddfd086ab6e44f353608b8efb7b2510a34ea1a..296286fc42967c8e8d2d8d31668fd48218fc9d68 100644
--- a/scipost_django/common/converters.py
+++ b/scipost_django/common/converters.py
@@ -20,7 +20,7 @@ class FourDigitYearConverter:
 
 
 class TwoDigitMonthConverter:
-    regex = '(0[1-9]{1})|(1[1-2]{1})'
+    regex = '0[1-9]|1[0-2]'
 
     def to_python(self, value):
         return int(value)
@@ -30,7 +30,7 @@ class TwoDigitMonthConverter:
 
 
 class TwoDigitDayConverter:
-    regex = '([0-2]{1}[1-9])|30|31'
+    regex = '0[1-9]|[1-2][0-9]|3[0-1]'
 
     def to_python(self, value):
         return int(value)