diff --git a/src/ViewportWidget.cpp b/src/ViewportWidget.cpp
index 17d7099..6ad5f91 100644
--- a/src/ViewportWidget.cpp
+++ b/src/ViewportWidget.cpp
@@ -383,7 +383,7 @@ void ViewportWidget::paintGL()
                 perpVec = QVector3D(0, -lineVec.z(), lineVec.y()).normalized();
             }
 
-            if (angleDiff >= 0) {
+            if (angleDiff < 0) {
                 perpVec = -perpVec;
             }
 
@@ -720,7 +720,7 @@ void ViewportWidget::paintGL()
                 perpVec = QVector3D(0, -lineVec.z(), lineVec.y()).normalized();
             }
 
-            if (angleDiff >= 0) {
+            if (angleDiff < 0) {
                 perpVec = -perpVec;
             }