diff --git a/Makefile.am b/Makefile.am
index f5d07e80abcb4b2cedd5a1537a3d9f2995aa1b0e..3e24fdb6ff8965fcd51d42b5ca531a5b84e1fc02 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,7 +8,7 @@ openfortivpn_SOURCES = src/config.c src/config.h src/hdlc.c src/hdlc.h \
 		       src/xml.h src/userinput.c src/userinput.h \
 		       src/openssl_hostname_validation.c \
 		       src/openssl_hostname_validation.h
-openfortivpn_CFLAGS = -Wall -pedantic -std=gnu99
+openfortivpn_CFLAGS = -Wall -pedantic
 openfortivpn_CPPFLAGS = -DSYSCONFDIR=\"$(sysconfdir)\" \
 			-DPPP_PATH=\"@PPP_PATH@\" \
 			-DNETSTAT_PATH=\"@NETSTAT_PATH@\" \
diff --git a/configure.ac b/configure.ac
index bce0947562a3971faffd79dd1cf3cb05e1ea0a15..fa51c845a09f6c511c5372e908c68718e3c4dfcd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -8,6 +8,7 @@ AM_INIT_AUTOMAKE([foreign subdir-objects])
 
 # Checks for programs.
 AC_PROG_CC
+AC_PROG_CC_STDC
 AC_PROG_MKDIR_P
 AC_PROG_SED
 AC_PROG_INSTALL