diff --git a/src/ViewportWidget.cpp b/src/ViewportWidget.cpp
index c8cf913..2de9b2a 100644
--- a/src/ViewportWidget.cpp
+++ b/src/ViewportWidget.cpp
@@ -735,6 +735,11 @@ void ViewportWidget::paintGL()
                 lineAngle = atan2(lineVec.z(), lineVec.y());
             }
 
+            double angleDiff = lineAngle - refAngle;
+            while (angleDiff <= -M_PI) angleDiff += 2 * M_PI;
+            while (angleDiff > M_PI) angleDiff -= 2 * M_PI;
+            lineAngle = refAngle + angleDiff;
+
             double angleDiffDegrees = qRadiansToDegrees(lineAngle - refAngle);
             while (angleDiffDegrees <= -180.0) angleDiffDegrees += 360.0;
             while (angleDiffDegrees > 180.0) angleDiffDegrees -= 360.0;