diff --git a/src/starkware/crypto/signature/math_utils.py b/src/starkware/crypto/signature/math_utils.py
index 2dc3a4d4..bf550fe9 100644
--- a/src/starkware/crypto/signature/math_utils.py
+++ b/src/starkware/crypto/signature/math_utils.py
@@ -29,6 +29,8 @@ def pi_as_string(digits: int) -> str:
     """
     Returns pi as a string of decimal digits without the decimal point ("314...").
     """
+    if digits < 0:
+        raise ValueError("Negative number of digits")
     mpmath.mp.dps = digits  # Set number of digits.
     return "3" + str(mpmath.mp.pi)[2:]
 
diff --git a/src/starkware/python/math_utils.py b/src/starkware/python/math_utils.py
index b676f85b..5181c697 100644
--- a/src/starkware/python/math_utils.py
+++ b/src/starkware/python/math_utils.py
@@ -19,8 +19,9 @@ def safe_div(x: int, y: int):
 
 
 def div_ceil(x, y):
-    assert isinstance(x, int) and isinstance(y, int)
-    return -((-x) // y)
+    if not isinstance(x, int) or not isinstance(y, int):
+        raise TypeError("Arguments must be integers.")
+    return (x + y - 1) // y
 
 
 def div_mod(n, m, p):