diff --git a/stdnum/lei.py b/stdnum/lei.py
index 06b5c524..36dbd9b5 100644
--- a/stdnum/lei.py
+++ b/stdnum/lei.py
@@ -42,7 +42,7 @@
 
 from stdnum.exceptions import *
 from stdnum.iso7064 import mod_97_10
-from stdnum.util import clean
+from stdnum.util import clean, isdigits
 
 
 def compact(number: str) -> str:
@@ -55,6 +55,12 @@ def validate(number: str) -> str:
     """Check if the number is valid. This checks the length, format and check
     digits."""
     number = compact(number)
+    if not all(x in '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ' for x in number):
+        raise InvalidFormat()
+    if len(number) != 20:
+        raise InvalidLength()
+    if not isdigits(number[-2:]):
+        raise InvalidFormat()
     mod_97_10.validate(number)
     return number
 
diff --git a/tests/test_lei.doctest b/tests/test_lei.doctest
index bc2d5a5b..4a055fe9 100644
--- a/tests/test_lei.doctest
+++ b/tests/test_lei.doctest
@@ -22,6 +22,29 @@ This file contains more detailed doctests for the stdnum.lei module.
 >>> from stdnum.exceptions import *
 
 
+The number should be exactly 20 characters long. Leading zeros change the
+length but not the checksum.
+
+>>> lei.validate('213800KUD8LAJWSQ9D15')
+'213800KUD8LAJWSQ9D15'
+>>> lei.validate('0213800KUD8LAJWSQ9D15')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+>>> lei.validate('1')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+
+
+The last two characters are the check digits and should be numeric.
+
+>>> lei.validate('213800KUD8LAJWSQ9DAD')
+Traceback (most recent call last):
+    ...
+InvalidFormat: ...
+
+
 These have been found online and should all be valid numbers.
 
 >>> numbers = '''