diff --git a/src/OpenMesh/Core/IO/writer/STLWriter.cc b/src/OpenMesh/Core/IO/writer/STLWriter.cc
index a9f86b7e..29fa185b 100644
--- a/src/OpenMesh/Core/IO/writer/STLWriter.cc
+++ b/src/OpenMesh/Core/IO/writer/STLWriter.cc
@@ -139,7 +139,7 @@ write(std::ostream& _os, BaseExporter& _be, const Options& _writeOptions, std::s
 
 bool
 _STLWriter_::
-write_stla(const std::string& _filename, BaseExporter& _be, Options /* _opt */) const
+write_stla(const std::string& _filename, const BaseExporter& _be, Options /* _opt */) const
 {
   omlog() << "[STLWriter] : write ascii file\n";
 
@@ -204,7 +204,7 @@ write_stla(const std::string& _filename, BaseExporter& _be, Options /* _opt */)
 
 bool
 _STLWriter_::
-write_stla(std::ostream& _out, BaseExporter& _be, Options /* _opt */, std::streamsize _precision) const
+write_stla(std::ostream& _out, const BaseExporter& _be, Options /* _opt */, std::streamsize _precision) const
 {
   omlog() << "[STLWriter] : write ascii file\n";
 
@@ -256,7 +256,7 @@ write_stla(std::ostream& _out, BaseExporter& _be, Options /* _opt */, std::strea
 
 bool
 _STLWriter_::
-write_stlb(const std::string& _filename, BaseExporter& _be, Options /* _opt */) const
+write_stlb(const std::string& _filename, const BaseExporter& _be, Options /* _opt */) const
 {
   omlog() << "[STLWriter] : write binary file\n";
 
@@ -336,7 +336,7 @@ write_stlb(const std::string& _filename, BaseExporter& _be, Options /* _opt */)
 
 bool
 _STLWriter_::
-write_stlb(std::ostream& _out, BaseExporter& _be, Options /* _opt */, std::streamsize _precision) const
+write_stlb(std::ostream& _out, const BaseExporter& _be, Options /* _opt */, std::streamsize _precision) const
 {
   omlog() << "[STLWriter] : write binary file\n";
 
diff --git a/src/OpenMesh/Core/IO/writer/STLWriter.hh b/src/OpenMesh/Core/IO/writer/STLWriter.hh
index 3c258299..2deaa7ec 100644
--- a/src/OpenMesh/Core/IO/writer/STLWriter.hh
+++ b/src/OpenMesh/Core/IO/writer/STLWriter.hh
@@ -98,10 +98,10 @@ public:
   size_t binary_size(BaseExporter&, const Options&) const override;
 
 private:
-  bool write_stla(const std::string&, BaseExporter&, Options) const;
-  bool write_stla(std::ostream&, BaseExporter&, Options, std::streamsize _precision = 6) const;
-  bool write_stlb(const std::string&, BaseExporter&, Options) const;
-  bool write_stlb(std::ostream&, BaseExporter&, Options, std::streamsize _precision = 6) const;
+  bool write_stla(const std::string&, const BaseExporter&, Options) const;
+  bool write_stla(std::ostream&, const BaseExporter&, Options, std::streamsize _precision = 6) const;
+  bool write_stlb(const std::string&, const BaseExporter&, Options) const;
+  bool write_stlb(std::ostream&, const BaseExporter&, Options, std::streamsize _precision = 6) const;
 };