diff --git a/include/boost/gil/extension/io/png_tags.hpp b/include/boost/gil/extension/io/png_tags.hpp
index 049cca64f..78a119558 100644
--- a/include/boost/gil/extension/io/png_tags.hpp
+++ b/include/boost/gil/extension/io/png_tags.hpp
@@ -22,8 +22,8 @@
 #ifdef BOOST_GIL_IO_PNG_FLOATING_POINT_SUPPORTED
 #ifdef BOOST_GIL_IO_PNG_FIXED_POINT_SUPPORTED
 # error "Cannot set both symbols"
-#endif BOOST_GIL_IO_PNG_FIXED_POINT_SUPPORTED
-#endif BOOST_GIL_IO_PNG_FLOATING_POINT_SUPPORTED
+#endif // BOOST_GIL_IO_PNG_FIXED_POINT_SUPPORTED
+#endif // BOOST_GIL_IO_PNG_FLOATING_POINT_SUPPORTED
 
 #ifndef BOOST_GIL_EXTENSION_IO_PNG_C_LIB_COMPILED_AS_CPLUSPLUS
     extern "C" {