diff --git a/maths/series/arithmetic_mean.py b/maths/series/arithmetic_mean.py
index 994f479d1..2519a8a35 100644
--- a/maths/series/arithmetic_mean.py
+++ b/maths/series/arithmetic_mean.py
@@ -27,6 +27,10 @@ def arithmetic_mean(series: list) -> float:
     4.0
     >>> arithmetic_mean([3, 6, 9, 12])
     7.5
+    >>> arithmetic_mean(4)
+    Traceback (most recent call last):
+        ...
+    ValueError: Input series is not valid, valid series - [2, 4, 6]
     >>> arithmetic_mean([4, 8, 1])
     Traceback (most recent call last):
         ...
@@ -39,13 +43,15 @@ def arithmetic_mean(series: list) -> float:
     ValueError: Input list must be a non empty list
 
     """
+    if not isinstance(series, list):
+        raise ValueError("Input series is not valid, valid series - [2, 4, 6]")
     if len(series) == 0:
         raise ValueError("Input list must be a non empty list")
     if not is_arithmetic_series(series):
         raise ValueError("Input list is not an arithmetic series")
     answer = 0
-    for _ in series:
-        answer += _
+    for val in series:
+        answer += val
     return answer / len(series)