diff --git a/bgpd/Makefile.am b/bgpd/Makefile.am
index 8a410adca16f..67613891002a 100644
--- a/bgpd/Makefile.am
+++ b/bgpd/Makefile.am
@@ -116,7 +116,7 @@ module_LTLIBRARIES += bgpd_snmp.la
 endif
 
 bgpd_snmp_la_SOURCES = bgp_snmp.c
-bgpd_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS)
+bgpd_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS) -std=gnu99
 bgpd_snmp_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
 bgpd_snmp_la_LIBADD = ../lib/libfrrsnmp.la
 
diff --git a/lib/subdir.am b/lib/subdir.am
index c5719786d62a..1c3d31b9278c 100644
--- a/lib/subdir.am
+++ b/lib/subdir.am
@@ -190,7 +190,7 @@ if SNMP
 lib_LTLIBRARIES += lib/libfrrsnmp.la
 endif
 
-lib_libfrrsnmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS)
+lib_libfrrsnmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS) -std=gnu99
 lib_libfrrsnmp_la_LDFLAGS = -version-info 0:0:0
 lib_libfrrsnmp_la_LIBADD = lib/libfrr.la $(SNMP_LIBS)
 lib_libfrrsnmp_la_SOURCES = \
diff --git a/ospf6d/subdir.am b/ospf6d/subdir.am
index 76a64cd63718..8a6c4a5ccfd3 100644
--- a/ospf6d/subdir.am
+++ b/ospf6d/subdir.am
@@ -61,6 +61,6 @@ ospf6d_ospf6d_SOURCES = \
 	# end
 
 ospf6d_ospf6d_snmp_la_SOURCES = ospf6d/ospf6_snmp.c
-ospf6d_ospf6d_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS)
+ospf6d_ospf6d_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS) -std=gnu99
 ospf6d_ospf6d_snmp_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
 ospf6d_ospf6d_snmp_la_LIBADD = lib/libfrrsnmp.la
diff --git a/ospfd/subdir.am b/ospfd/subdir.am
index 9f04260366a1..f2e292e186b5 100644
--- a/ospfd/subdir.am
+++ b/ospfd/subdir.am
@@ -89,7 +89,7 @@ ospfd_ospfd_LDADD = ospfd/libfrrospf.a lib/libfrr.la @LIBCAP@ @LIBM@
 ospfd_ospfd_SOURCES = ospfd/ospf_main.c
 
 ospfd_ospfd_snmp_la_SOURCES = ospfd/ospf_snmp.c
-ospfd_ospfd_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS)
+ospfd_ospfd_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS) -std=gnu99
 ospfd_ospfd_snmp_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
 ospfd_ospfd_snmp_la_LIBADD = lib/libfrrsnmp.la
 
diff --git a/ripd/subdir.am b/ripd/subdir.am
index 7a8f2185baaa..1c5167ef4a12 100644
--- a/ripd/subdir.am
+++ b/ripd/subdir.am
@@ -35,7 +35,7 @@ ripd_ripd_SOURCES = \
 	# end
 
 ripd_ripd_snmp_la_SOURCES = ripd/rip_snmp.c
-ripd_ripd_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS)
+ripd_ripd_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS) -std=gnu99
 ripd_ripd_snmp_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
 ripd_ripd_snmp_la_LIBADD = lib/libfrrsnmp.la
 
diff --git a/zebra/subdir.am b/zebra/subdir.am
index 45e285a9e7f3..d3abcef6d5fe 100644
--- a/zebra/subdir.am
+++ b/zebra/subdir.am
@@ -127,7 +127,7 @@ zebra_zebra_irdp_la_SOURCES = \
 zebra_zebra_irdp_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
 
 zebra_zebra_snmp_la_SOURCES = zebra/zebra_snmp.c
-zebra_zebra_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS)
+zebra_zebra_snmp_la_CFLAGS = $(WERROR) $(SNMP_CFLAGS) -std=gnu99
 zebra_zebra_snmp_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
 zebra_zebra_snmp_la_LIBADD = lib/libfrrsnmp.la