diff --git a/Makefile b/Makefile
index 6b7751f..f33f88e 100644
--- a/Makefile
+++ b/Makefile
@@ -20,7 +20,8 @@ endef
 CPPFLAGS := $(CPPFLAGS) -D_GNU_SOURCE -I include
 SHARED_FLAGS := -pipe -O3 -flto -fPIC -fvisibility=hidden -fno-plt \
     -fstack-clash-protection $(call safe_flag,-fcf-protection) -fstack-protector-strong \
-    -Wall -Wextra $(call safe_flag,-Wcast-align=strict,-Wcast-align) -Wcast-qual -Wwrite-strings
+    -Wall -Wextra $(call safe_flag,-Wcast-align=strict,-Wcast-align) -Wcast-qual -Wwrite-strings \
+    -Wundef
 
 ifeq ($(CONFIG_WERROR),true)
     SHARED_FLAGS += -Werror