diff --git a/src/Magnum/Shaders/Line.frag b/src/Magnum/Shaders/Line.frag
index 18d42bd03..18ecb3f41 100644
--- a/src/Magnum/Shaders/Line.frag
+++ b/src/Magnum/Shaders/Line.frag
@@ -166,7 +166,7 @@ layout(std140
 noperspective
 #endif
 in highp vec2 centerDistanceSigned;
-in highp float halfSegmentLength;
+flat in highp float halfSegmentLength;
 #ifdef CAN_USE_NOPERSPECTIVE
 noperspective
 #endif
diff --git a/src/Magnum/Shaders/Line.vert b/src/Magnum/Shaders/Line.vert
index e1c4d59d9..e6e5221f2 100644
--- a/src/Magnum/Shaders/Line.vert
+++ b/src/Magnum/Shaders/Line.vert
@@ -274,7 +274,7 @@ in highp mat4 instancedTransformationMatrix;
 noperspective
 #endif
 out highp vec2 centerDistanceSigned;
-out highp float halfSegmentLength;
+flat out highp float halfSegmentLength;
 #ifdef CAN_USE_NOPERSPECTIVE
 noperspective
 #endif