diff --git a/Makefile b/Makefile
index d352358a0..02592df98 100644
--- a/Makefile
+++ b/Makefile
@@ -608,6 +608,11 @@ $(eval $(call add_include_file,backends/cxxrtl/cxxrtl_vcd_capi.cc))
 $(eval $(call add_include_file,backends/cxxrtl/cxxrtl_vcd_capi.h))
 
 OBJS += kernel/driver.o kernel/register.o kernel/rtlil.o kernel/log.o kernel/calc.o kernel/yosys.o
+ifeq ($(ENABLE_ABC),1)
+ifneq ($(ABCEXTERNAL),)
+kernel/yosys.o: CXXFLAGS += -DABCEXTERNAL='"$(ABCEXTERNAL)"'
+endif
+endif
 OBJS += kernel/cellaigs.o kernel/celledges.o kernel/satgen.o kernel/mem.o
 
 kernel/log.o: CXXFLAGS += -DYOSYS_SRC='"$(YOSYS_SRC)"'