diff --git a/Makefile.am b/Makefile.am
index 6325a438..295370a3 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -41,8 +41,8 @@ if BUILD_FOR_OPENBSD
   AM_CXXFLAGS = -I/usr/local/include -Wno-multichar -Wall -Wextra -Wno-clobbered -Wno-psabi -pthread -DSYSCONFDIR=\"$(sysconfdir)\"
   AM_CFLAGS = --include=utilities/debug.h -Wno-multichar -Wall -Wextra -pthread -DSYSCONFDIR=\"$(sysconfdir)\"
 else
-  AM_CXXFLAGS = -Wshadow -fno-common -Wno-multichar -Wall -Wextra -Wno-clobbered -Wno-psabi -pthread -DSYSCONFDIR=\"$(sysconfdir)\"
-  AM_CFLAGS = --include=utilities/debug.h -Wshadow -fno-common -Wno-multichar -Wall -Wextra -Wno-clobbered -Wno-psabi -pthread -DSYSCONFDIR=\"$(sysconfdir)\"
+  AM_CXXFLAGS = -Wshadow -fno-common -Wno-multichar -Wall -Wextra -Wformat -Wno-clobbered -Wno-psabi -pthread -DSYSCONFDIR=\"$(sysconfdir)\"
+  AM_CFLAGS = --include=utilities/debug.h -Wshadow -fno-common -Wno-multichar -Wall -Wextra -Wformat -Wno-clobbered -Wno-psabi -pthread -DSYSCONFDIR=\"$(sysconfdir)\"
 endif
 endif
 endif