diff --git a/scripts/mbedtls_dev/bignum_common.py b/scripts/mbedtls_dev/bignum_common.py
index 81bc28e19a03..3ff8b2f35bc9 100644
--- a/scripts/mbedtls_dev/bignum_common.py
+++ b/scripts/mbedtls_dev/bignum_common.py
@@ -251,10 +251,10 @@ def __init__(self, val_n: str, val_a: str, val_b: str = "0",
         # provides earlier/more robust input validation.
         self.int_n = hex_to_int(val_n)
 
-    def to_montgomery(self, val) -> int:
+    def to_montgomery(self, val: int) -> int:
         return (val * self.r) % self.int_n
 
-    def from_montgomery(self, val) -> int:
+    def from_montgomery(self, val: int) -> int:
         return (val * self.r_inv) % self.int_n
 
     @property