diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index 1b9d89c807..70f589b35a 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -1589,6 +1589,11 @@ const char *proj_as_wkt(PJ_CONTEXT *ctx, const PJ *obj, PJ_WKT_TYPE type,
  * The returned string is valid while the input obj parameter is valid,
  * and until a next call to proj_as_proj_string() with the same input
  * object.
+ * 
+ * \warning If a CRS object was not created from a PROJ string, 
+ *          exporting to a PROJ string will in most cases
+ *          cause a loss of information. This can potentially lead to
+ *          erroneous transformations.
  *
  * This function calls
  * osgeo::proj::io::IPROJStringExportable::exportToPROJString().