diff --git a/strings/palindrome.py b/strings/palindrome.py
index 4df5639b0c49..7a513942c43d 100644
--- a/strings/palindrome.py
+++ b/strings/palindrome.py
@@ -24,8 +24,15 @@ def is_palindrome(s: str) -> bool:
 
     >>> all(is_palindrome(key) == value for key, value in test_data.items())
     True
+    >>> is_palindrome(123)
+    Traceback (most recent call last):
+        ...
+    TypeError: Input must be a string
     """
 
+    if not isinstance(s, str):
+        raise TypeError("Input must be a string")
+
     start_i = 0
     end_i = len(s) - 1
     while start_i < end_i:
@@ -44,6 +51,9 @@ def is_palindrome_traversal(s: str) -> bool:
     >>> all(is_palindrome_traversal(key) == value for key, value in test_data.items())
     True
     """
+    if not isinstance(s, str):
+        raise TypeError("Input must be a string")
+
     end = len(s) // 2
     n = len(s)
 
@@ -63,6 +73,9 @@ def is_palindrome_recursive(s: str) -> bool:
     >>> all(is_palindrome_recursive(key) == value for key, value in test_data.items())
     True
     """
+    if not isinstance(s, str):
+        raise TypeError("Input must be a string")
+
     if len(s) <= 1:
         return True
     if s[0] == s[len(s) - 1]:
@@ -78,6 +91,9 @@ def is_palindrome_slice(s: str) -> bool:
     >>> all(is_palindrome_slice(key) == value for key, value in test_data.items())
     True
     """
+    if not isinstance(s, str):
+        raise TypeError("Input must be a string")
+
     return s == s[::-1]
 
 
diff --git a/strings/reverse_letters.py b/strings/reverse_letters.py
index cd1b7832d066..770796f8110e 100644
--- a/strings/reverse_letters.py
+++ b/strings/reverse_letters.py
@@ -12,6 +12,12 @@ def reverse_letters(sentence: str, length: int = 0) -> str:
     >>> reverse_letters("racecar")
     'racecar'
     """
+    if not isinstance(sentence, str):
+        raise TypeError("sentence must be a string")
+
+    if not isinstance(length, int) or length < 0:
+        raise ValueError("length must be a non-negative integer")
+
     return " ".join(
         word[::-1] if len(word) > length else word for word in sentence.split()
     )