diff --git a/xs/src/libslic3r/SurfaceCollection.cpp b/xs/src/libslic3r/SurfaceCollection.cpp
index b8eb7bb22..45f805c73 100644
--- a/xs/src/libslic3r/SurfaceCollection.cpp
+++ b/xs/src/libslic3r/SurfaceCollection.cpp
@@ -214,4 +214,4 @@ SurfaceCollection::group(std::vector<SurfacesPtr> *retval)
 
 
 
-}
+} // namespace Slic3r
diff --git a/xs/src/libslic3r/SurfaceCollection.hpp b/xs/src/libslic3r/SurfaceCollection.hpp
index a12aecec0..085c16b68 100644
--- a/xs/src/libslic3r/SurfaceCollection.hpp
+++ b/xs/src/libslic3r/SurfaceCollection.hpp
@@ -36,9 +36,13 @@ class SurfaceCollection
     /// group surfaces by common properties
     void group(std::vector<SurfacesPtr> *retval);
 
+    /// Deletes every surface other than the ones that match the provided type.
     void keep_type(const SurfaceType type);
+    /// Deletes every surface other than the ones that match the provided types.
     void keep_types(std::initializer_list<SurfaceType> types);
-    void keep_types(const SurfaceType *types, int ntypes);
+
+    /// Deletes every surface other than the ones that match the provided types.
+    void keep_types(const SurfaceType *types, size_t ntypes);
 
     /// deletes all surfaces that match the supplied aggregate of types.
     void remove_types(const SurfaceType *types, size_t ntypes);