diff --git a/drone_test/__init__.py b/drone_test/__init__.py
index 936bd02..a35fa4e 100644
--- a/drone_test/__init__.py
+++ b/drone_test/__init__.py
@@ -9,4 +9,7 @@ def circle_area(radius: float):
     :raises ValueError: radius is negative
     :return: area of the circle
     """
+    if radius < 0:
+        raise ValueError("Circle can't have negative radius")
+
     return math.pi * radius ** 2