diff --git a/configure b/configure
index e5fab36f..5edd42f0 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #!/bin/sh
-# $Id: configure,v 1.18 2009-07-14 06:47:12 nicm Exp $
+# $Id: configure,v 1.19 2009-07-31 10:30:40 nicm Exp $
 
 TMUX_PLATFORM=${TMUX_PLATFORM:-`uname -s`}
 
@@ -82,7 +82,7 @@ SRCS+= osdep-linux.c \
 	compat/strtonum.c \
         compat/getopt.c \
 	compat/vis.c
-CFLAGS+= -D_GNU_SOURCE -D_POSIX_SOURCE
+CFLAGS+= -std=c99 -D_GNU_SOURCE -D_POSIX_SOURCE
 LIBS+= -lcrypt -lutil
 EOF
 	;;