diff --git a/src/libslic3r/FaceDetector.cpp b/src/libslic3r/FaceDetector.cpp
index 33423ae7e..5eb5ca762 100644
--- a/src/libslic3r/FaceDetector.cpp
+++ b/src/libslic3r/FaceDetector.cpp
@@ -2,6 +2,7 @@
 #include "TriangleMesh.hpp"
 #include "SLA/IndexedMesh.hpp"
 #include "Model.hpp"
+#include <unordered_set>
 
 namespace Slic3r {
 static const double BBOX_OFFSET = 2.0;