diff --git a/src/libslic3r/Arachne/SkeletalTrapezoidationGraph.hpp b/src/libslic3r/Arachne/SkeletalTrapezoidationGraph.hpp
index cfdbfecda..efda32383 100644
--- a/src/libslic3r/Arachne/SkeletalTrapezoidationGraph.hpp
+++ b/src/libslic3r/Arachne/SkeletalTrapezoidationGraph.hpp
@@ -10,6 +10,11 @@
 #include "SkeletalTrapezoidationEdge.hpp"
 #include "SkeletalTrapezoidationJoint.hpp"
 
+namespace Slic3r
+{
+class Line;
+};
+
 namespace Slic3r::Arachne
 {