diff --git a/include/assimp/Exporter.hpp b/include/assimp/Exporter.hpp
index 30db01508..20cd7dc6e 100644
--- a/include/assimp/Exporter.hpp
+++ b/include/assimp/Exporter.hpp
@@ -51,6 +51,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 namespace Assimp	{
 	class ExporterPimpl;
+	class IOSystem;
 
 
 // ----------------------------------------------------------------------------------