diff --git a/Makefile b/Makefile
index 543ec7f44..e95d6cace 100644
--- a/Makefile
+++ b/Makefile
@@ -104,7 +104,7 @@ VPATH := $(YOSYS_SRC)
 UNITESTPATH := $(YOSYS_SRC)/tests/unit
 
 export CXXSTD ?= c++17
-CXXFLAGS := $(CXXFLAGS) -Wall -Wextra -ggdb -I. -I"$(YOSYS_SRC)" -MD -MP -D_YOSYS_ -fPIC -I$(PREFIX)/include
+CXXFLAGS := $(CXXFLAGS) -Wall -Wextra -Werror=unused -ggdb -I. -I"$(YOSYS_SRC)" -MD -MP -D_YOSYS_ -fPIC -I$(PREFIX)/include
 LIBS := $(LIBS) -lstdc++ -lm
 PLUGIN_LINKFLAGS :=
 PLUGIN_LIBS :=