diff --git a/Makefile b/Makefile
index e08a3f6..7a21d12 100644
--- a/Makefile
+++ b/Makefile
@@ -30,7 +30,7 @@
 DIFF    = diff
 PREFIX  ?= /usr/local
 MANDIR  ?= $(PREFIX)/share/man
-CFLAGS  ?= -Os -Wall -Wshadow
+CFLAGS  ?= -Os -Wall -Wshadow -Wmissing-prototypes
 EXPORTDIR ?= .
 RANLIB  ?= ranlib
 PKG_CONFIG ?= pkg-config