diff --git a/core/msdfgen-c.cpp b/core/msdfgen-c.cpp
index e7cce33..9b802c4 100644
--- a/core/msdfgen-c.cpp
+++ b/core/msdfgen-c.cpp
@@ -205,11 +205,11 @@ MSDF_API int msdf_shape_get_bounds(msdf_shape_const_handle shape, msdf_bounds_t*
     return MSDF_SUCCESS;
 }
 
-MSDF_API int msdf_shape_add_contour(msdf_shape_handle shape, msdf_contour_handle contour) {
+MSDF_API int msdf_shape_add_contour(msdf_shape_handle shape, msdf_contour_const_handle contour) {
     if(shape == nullptr || contour == nullptr) {
         return MSDF_ERR_INVALID_ARG;
     }
-    reinterpret_cast<msdfgen::Shape*>(shape)->addContour(*reinterpret_cast<msdfgen::Contour*>(contour));
+    reinterpret_cast<msdfgen::Shape*>(shape)->addContour(*reinterpret_cast<const msdfgen::Contour*>(contour));
     return MSDF_SUCCESS;
 }
 
diff --git a/msdfgen-c.h b/msdfgen-c.h
index f668e66..67ab638 100644
--- a/msdfgen-c.h
+++ b/msdfgen-c.h
@@ -221,7 +221,7 @@ MSDF_API int msdf_shape_get_bounds(msdf_shape_const_handle shape, msdf_bounds_t*
  * @param contour A pointer to the contour to add to the shape.
  * @returns @code MSDF_SUCCESS@endcode on success, otherwise one of the constants prefixed with @code MSDF_ERR_@endcode.
  */
-MSDF_API int msdf_shape_add_contour(msdf_shape_handle shape, msdf_contour_handle contour);
+MSDF_API int msdf_shape_add_contour(msdf_shape_handle shape, msdf_contour_const_handle contour);
 
 /**
  * Retrieves the number of contours allocated within the given shape object.