diff --git a/tests/extmod/uhashlib_sha256.py b/tests/extmod/uhashlib_sha256.py
index 3200e8f5c..676d47979 100644
--- a/tests/extmod/uhashlib_sha256.py
+++ b/tests/extmod/uhashlib_sha256.py
@@ -23,6 +23,9 @@ print(h.digest())
 
 print(hashlib.sha256(b"\xff" * 64).digest())
 
+# 56 bytes is a boundary case in the algorithm
+print(hashlib.sha256(b"\xff" * 56).digest())
+
 # TODO: running .digest() several times in row is not supported()
 #h = hashlib.sha256(b'123')
 #print(h.digest())