diff --git a/api/s32_region_util.py b/api/s32_region_util.py
index d193063..cab8ac6 100644
--- a/api/s32_region_util.py
+++ b/api/s32_region_util.py
@@ -73,11 +73,11 @@ def _angle(v: tuple[float, float]) -> float:
     if v[0] >= 0 and v[1] >= 0:
         return math.asin(v[1])
     elif v[0] <= 0 and v[1] >= 0:
-        return math.asin(v[1]) + math.pi * 0.5
+        return math.pi - math.asin(v[1])
     elif v[0] <= 0 and v[1] <= 0:
         return math.asin(-v[1]) + math.pi
     elif v[0] >= 0 and v[1] <= 0:
-        return math.asin(-v[1]) + math.pi * 1.5
+        return math.pi * 2 - math.asin(-v[1])
     return 0