diff --git a/xs/src/libslic3r/TransformationMatrix.cpp b/xs/src/libslic3r/TransformationMatrix.cpp
index e46962e7a..efd77d083 100644
--- a/xs/src/libslic3r/TransformationMatrix.cpp
+++ b/xs/src/libslic3r/TransformationMatrix.cpp
@@ -117,7 +117,7 @@ void TransformationMatrix::applyLeft(const TransformationMatrix &left)
     *this = temp;
 }
 
-TransformationMatrix TransformationMatrix::multiplyLeft(const TransformationMatrix &left)
+TransformationMatrix TransformationMatrix::multiplyLeft(const TransformationMatrix &left) const
 {
     return multiply(left, *this);
 }
@@ -128,7 +128,7 @@ void TransformationMatrix::applyRight(const TransformationMatrix &right)
     *this = temp;
 }
 
-TransformationMatrix TransformationMatrix::multiplyRight(const TransformationMatrix &right)
+TransformationMatrix TransformationMatrix::multiplyRight(const TransformationMatrix &right) const
 {
     return multiply(*this, right);
 }
diff --git a/xs/src/libslic3r/TransformationMatrix.hpp b/xs/src/libslic3r/TransformationMatrix.hpp
index f7876c67a..b2bd545f8 100644
--- a/xs/src/libslic3r/TransformationMatrix.hpp
+++ b/xs/src/libslic3r/TransformationMatrix.hpp
@@ -39,13 +39,13 @@ public:
     void applyLeft(const TransformationMatrix &left);
 
     /// multiplies the parameter-matrix from the left (out=left*this)
-    TransformationMatrix multiplyLeft(const TransformationMatrix &left);
+    TransformationMatrix multiplyLeft(const TransformationMatrix &left) const;
 
     /// multiplies the parameter-matrix from the right (this=this*right)
     void applyRight(const TransformationMatrix &right);
 
     /// multiplies the parameter-matrix from the right (out=this*right)
-    TransformationMatrix multiplyRight(const TransformationMatrix &right);
+    TransformationMatrix multiplyRight(const TransformationMatrix &right) const;
 
     /// generates an eye matrix.
     static TransformationMatrix mat_eye();