diff --git a/src/Magnum/Shaders/Implementation/lineMiterLimit.h b/src/Magnum/Shaders/Implementation/lineMiterLimit.h
index 7ce223aa1..53ad972cb 100644
--- a/src/Magnum/Shaders/Implementation/lineMiterLimit.h
+++ b/src/Magnum/Shaders/Implementation/lineMiterLimit.h
@@ -32,6 +32,9 @@
 
 namespace Magnum { namespace Shaders { namespace Implementation {
 
+/* These helpers, along with tests, are copied verbatim between the Shaders and
+   Ui libraries */
+
 inline Float lineMiterLengthLimit(const char*
     #if !defined(CORRADE_NO_ASSERT) && !defined(CORRADE_STANDARD_ASSERT)
     const name
diff --git a/src/Magnum/Shaders/Line.h b/src/Magnum/Shaders/Line.h
index d10a1a73e..fd69817ee 100644
--- a/src/Magnum/Shaders/Line.h
+++ b/src/Magnum/Shaders/Line.h
@@ -46,6 +46,9 @@ namespace Magnum { namespace Shaders {
 @see @ref LineGL::capStyle(), @ref LineGL::Configuration::setCapStyle()
 */
 enum class LineCapStyle: UnsignedByte {
+    /* Keep these in sync with Ui::LineCapStyle (except for the related links,
+       of course). The images are used directly from there. */
+
     /**
      * [Butt cap](https://en.wikipedia.org/wiki/Butt_joint). The line is cut
      * off right at the endpoint. Lines of zero length will be invisible.
@@ -95,6 +98,9 @@ enum class LineCapStyle: UnsignedByte {
 @see @ref LineGL::joinStyle(), @ref LineGL::Configuration::setJoinStyle()
 */
 enum class LineJoinStyle: UnsignedByte {
+    /* Keep these in sync with Ui::LineJoinStyle (except for the related links,
+       of course). The images are used directly from there. */
+
     /**
      * [Miter join](https://en.wikipedia.org/wiki/Miter_joint). The outer edges
      * of both line segments extend until they intersect.
@@ -156,6 +162,9 @@ The type is 32-bit in order to match the default type of the
 bits.
 */
 enum class LineVertexAnnotation: UnsignedInt {
+    /* Keep these in sync with the internal Ui::LineLayer LineVertexAnnotation*
+       constants and ANNOTATION_* defines in Line.in.vert. */
+
     /**
      * The point extends upwards assuming a left-to-right direction of the line
      * segment. If not set, it extends downwards. Visualized as `U` in the
diff --git a/src/Magnum/Shaders/Line.in.frag b/src/Magnum/Shaders/Line.in.frag
index 913bbe430..034888b3a 100644
--- a/src/Magnum/Shaders/Line.in.frag
+++ b/src/Magnum/Shaders/Line.in.frag
@@ -24,6 +24,9 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+/* This file, along with *.in.vert, is copied verbatim between the Shaders
+   and Ui libraries */
+
 mediump float lineBlendFactor(
     in highp vec2 centerDistanceSigned,
     in highp float halfSegmentLength,
diff --git a/src/Magnum/Shaders/Line.in.vert b/src/Magnum/Shaders/Line.in.vert
index 8dbdeddeb..2f0073f03 100644
--- a/src/Magnum/Shaders/Line.in.vert
+++ b/src/Magnum/Shaders/Line.in.vert
@@ -24,6 +24,9 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+/* This file, along with *.in.frag, is copied verbatim between the Shaders
+   and Ui libraries */
+
 /* Point annotation, matching the LineVertexAnnotation enum bits */
 #define ANNOTATION_UP_MASK 1u
 #define ANNOTATION_JOIN_MASK 2u
diff --git a/src/Magnum/Shaders/LineGL.cpp b/src/Magnum/Shaders/LineGL.cpp
index b41c1e66b..9bbf9e572 100644
--- a/src/Magnum/Shaders/LineGL.cpp
+++ b/src/Magnum/Shaders/LineGL.cpp
@@ -124,7 +124,8 @@ template<UnsignedInt dimensions> typename LineGL<dimensions>::CompileState LineG
     #endif
 
     /* Cap and join style is needed by both the vertex and fragment shader,
-       prepare their defines just once for both */
+       prepare their defines just once for both. This snippet is shared between
+       Shaders::LineGL and Ui::LineLayerGL, keep in sync. */
     Containers::StringView capStyleDefine, joinStyleDefine;
     switch(configuration.capStyle()) {
         case LineCapStyle::Butt:
diff --git a/src/Magnum/Shaders/Test/LineTest.cpp b/src/Magnum/Shaders/Test/LineTest.cpp
index 3282379de..58995c75f 100644
--- a/src/Magnum/Shaders/Test/LineTest.cpp
+++ b/src/Magnum/Shaders/Test/LineTest.cpp
@@ -49,6 +49,8 @@ struct LineTest: TestSuite::Tester {
     void materialUniformConstructNoInit();
     void materialUniformSetters();
 
+    /* Miter limit tests are copied verbatim between the Shaders and Ui
+       libraries */
     void materialUniformMiterLimit();
     void materialUniformMiterLengthLimitInvalid();
     void materialUniformMiterAngleLimitInvalid();