diff --git a/xs/src/libslic3r/ClipperUtils.cpp b/xs/src/libslic3r/ClipperUtils.cpp
index 3d07891b1..f18653702 100644
--- a/xs/src/libslic3r/ClipperUtils.cpp
+++ b/xs/src/libslic3r/ClipperUtils.cpp
@@ -685,7 +685,7 @@ SV*
 polynode_children_2_perl(const ClipperLib::PolyNode& node)
 {
     AV* av = newAV();
-    const unsigned int len = node.ChildCount();
+    const int len = node.ChildCount();
     if (len > 0) av_extend(av, len-1);
     for (int i = 0; i < len; ++i) {
         av_store(av, i, polynode2perl(*node.Childs[i]));
diff --git a/xs/src/libslic3r/TriangleMesh.cpp b/xs/src/libslic3r/TriangleMesh.cpp
index 6e2f56312..743bf4584 100644
--- a/xs/src/libslic3r/TriangleMesh.cpp
+++ b/xs/src/libslic3r/TriangleMesh.cpp
@@ -429,7 +429,7 @@ void TriangleMesh::ReadFromPerl(SV* vertices, SV* facets)
     
     // read geometry
     AV* vertices_av = (AV*)SvRV(vertices);
-    for (unsigned int i = 0; i < stl.stats.number_of_facets; i++) {
+    for (int i = 0; i < stl.stats.number_of_facets; i++) {
         AV* facet_av = (AV*)SvRV(*av_fetch(facets_av, i, 0));
         stl_facet facet;
         facet.normal.x = 0;