diff --git a/software/mk/Makefile.builddefs b/software/mk/Makefile.builddefs
index ccdc94eda..7c97eac1a 100644
--- a/software/mk/Makefile.builddefs
+++ b/software/mk/Makefile.builddefs
@@ -132,6 +132,7 @@ endif
 BSG_MANYCORE_LIB_OBJS+= bsg_tile_config_vars.o
 BSG_MANYCORE_LIB_OBJS+= bsg_set_tile_x_y.o
 BSG_MANYCORE_LIB_OBJS+= bsg_printf.o
+BSG_MANYCORE_LIB_OBJS+= bsg_mcs_mutex.o
 
 BSG_MANYCORE_LIB = bsg_manycore_lib.a