2 files changed, 10 insertions, 0 deletions
diff --git a/build/flags.mk b/build/flags.mk
index 1421ce6..2562e03 100644
--- a/build/flags.mk
+++ b/build/flags.mk
@@ -88,6 +88,7 @@ AUTO_FLAGS := \
     gen/flags/Wshadow.mk \
     gen/flags/Wsign-compare.mk \
     gen/flags/Wstrict-prototypes.mk \
+    gen/flags/Wundef-prefix.mk \
     gen/flags/bind-now.mk \
     gen/flags/deps.mk
 
diff --git a/build/flags/Wundef-prefix.c b/build/flags/Wundef-prefix.c
new file mode 100644
index 0000000..3eaf82b
--- /dev/null
+++ b/build/flags/Wundef-prefix.c
@@ -0,0 +1,9 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+/// _CPPFLAGS += -Wundef-prefix=BFS_
+/// -Werror
+
+int main(void) {
+	return 0;
+}