diff --git a/src/DIRAC/Core/Security/test/Test_X509Chain.py b/src/DIRAC/Core/Security/test/Test_X509Chain.py
index 8f9db53e7bb..bd30201182e 100644
--- a/src/DIRAC/Core/Security/test/Test_X509Chain.py
+++ b/src/DIRAC/Core/Security/test/Test_X509Chain.py
@@ -61,7 +61,7 @@
 TWENTY_YEARS_IN_SEC = 20 * ONE_YEAR_IN_SECS
 
 # Validity date wont go further than 2050, See RFC 5280 4.1.2.5 for more information.
-NO_LATER_THAN_2050_IN_SEC = int((datetime.strptime("2049-12-31", "%Y-%M-%d") - datetime.now()).total_seconds())
+NO_LATER_THAN_2050_IN_SEC = int((datetime.strptime("2049-12-31", "%Y-%m-%d") - datetime.now()).total_seconds())
 
 
 @fixture(scope="function", params=X509CHAINTYPES)