diff --git a/config/Rules.am b/config/Rules.am
index 20a21e972b..1d39e7779a 100644
--- a/config/Rules.am
+++ b/config/Rules.am
@@ -5,6 +5,7 @@ AM_CFLAGS  = ${DEBUG_CFLAGS} -Wall -Wstrict-prototypes
 AM_CFLAGS += ${NO_UNUSED_BUT_SET_VARIABLE}
 AM_CFLAGS += ${NO_BOOL_COMPARE}
 AM_CFLAGS += -fno-strict-aliasing
+AM_CFLAGS += -std=gnu99
 AM_CPPFLAGS  = -D_GNU_SOURCE -D__EXTENSIONS__ -D_REENTRANT
 AM_CPPFLAGS += -D_POSIX_PTHREAD_SEMANTICS -D_FILE_OFFSET_BITS=64
 AM_CPPFLAGS += -D_LARGEFILE64_SOURCE -DHAVE_LARGE_STACKS=1
diff --git a/config/kernel.m4 b/config/kernel.m4
index a441328378..b8bd41e084 100644
--- a/config/kernel.m4
+++ b/config/kernel.m4
@@ -123,6 +123,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 
 	dnl # -Wall -fno-strict-aliasing -Wstrict-prototypes and other
 	dnl # compiler options are added by the kernel build system.
+	KERNELCPPFLAGS="$KERNELCPPFLAGS -std=gnu99"
 	KERNELCPPFLAGS="$KERNELCPPFLAGS -Wno-declaration-after-statement"
 	KERNELCPPFLAGS="$KERNELCPPFLAGS $NO_UNUSED_BUT_SET_VARIABLE"
 	KERNELCPPFLAGS="$KERNELCPPFLAGS $NO_BOOL_COMPARE"
diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index 0665c12fc0..2ea64a2bba 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -2956,7 +2956,6 @@ void
 dsl_dataset_clone_swap_sync_impl(dsl_dataset_t *clone,
     dsl_dataset_t *origin_head, dmu_tx_t *tx)
 {
-	spa_feature_t f;
 	dsl_pool_t *dp = dmu_tx_pool(tx);
 	int64_t unused_refres_delta;
 	blkptr_t tmp;
@@ -2974,7 +2973,7 @@ dsl_dataset_clone_swap_sync_impl(dsl_dataset_t *clone,
 	/*
 	 * Swap per-dataset feature flags.
 	 */
-	for (f = 0; f < SPA_FEATURES; f++) {
+	for (spa_feature_t f = 0; f < SPA_FEATURES; f++) {
 		boolean_t clone_inuse;
 		boolean_t origin_head_inuse;
 
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index e5cd47afd8..abe77ecd4b 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -65,7 +65,8 @@ static list_t zvol_state_list;
 #define	ZVOL_HT_SIZE	1024
 static struct hlist_head *zvol_htable;
 #define	ZVOL_HT_HEAD(hash)	(&zvol_htable[(hash) & (ZVOL_HT_SIZE-1)])
-static DEFINE_IDA(zvol_ida);
+
+static struct ida zvol_ida;
 
 /*
  * The in-core state of each volume.
@@ -2161,6 +2162,7 @@ zvol_init(void)
 	list_create(&zvol_state_list, sizeof (zvol_state_t),
 	    offsetof(zvol_state_t, zv_next));
 	mutex_init(&zvol_state_lock, NULL, MUTEX_DEFAULT, NULL);
+	ida_init(&zvol_ida);
 
 	zvol_htable = kmem_alloc(ZVOL_HT_SIZE * sizeof (struct hlist_head),
 	    KM_SLEEP);