diff --git a/Siv3D/src/Siv3D/Polygon/PolygonDetail.cpp b/Siv3D/src/Siv3D/Polygon/PolygonDetail.cpp
index cc62e0ead..9b7d167d6 100644
--- a/Siv3D/src/Siv3D/Polygon/PolygonDetail.cpp
+++ b/Siv3D/src/Siv3D/Polygon/PolygonDetail.cpp
@@ -1290,7 +1290,7 @@ namespace s3d
 
 		Polygon CalculateRoundBuffer(const LineString& points, const double distance, CloseRing closeRing, int32 bufferQuality)
 		{
-			if (points.size() < 2)
+			if (points.size() < 1)
 			{
 				return{};
 			}