diff --git a/src/lib/utility/utility.h b/src/lib/utility/utility.h
index d707da0b..f63128b4 100644
--- a/src/lib/utility/utility.h
+++ b/src/lib/utility/utility.h
@@ -39,7 +39,10 @@ namespace utility
 	template<typename T>
 	bool isPermutation(const std::vector<T>& a, const std::vector<T>& b)
 	{
-		return std::is_permutation(a.begin(), a.end(), b.begin());
+		return (
+			a.size() == b.size() && 
+			std::is_permutation(a.begin(), a.end(), b.begin())
+		);
 	}
 
 	bool intersectionPoint(Vec2f a1, Vec2f b1, Vec2f a2, Vec2f b2, Vec2f* i);