diff --git a/libraries/io/mdio/hdllib.cfg b/libraries/io/mdio/hdllib.cfg
index 0cb8a9f188d56bde9d09e695bea66021e9b98a3d..45d9a2e097a2a52be784c0e7aacfd1f02b1f4a5d 100644
--- a/libraries/io/mdio/hdllib.cfg
+++ b/libraries/io/mdio/hdllib.cfg
@@ -4,7 +4,7 @@ hdl_lib_uses = common mm
 hdl_lib_technology = 
 
 build_dir_sim = $HDL_BUILD_DIR
-build_dir_synth = 
+build_dir_synth = $HDL_BUILD_DIR
 
 synth_files =
     $UNB/Firmware/modules/Lofar/mdio/src/vhdl/mdio_pkg.vhd