diff --git a/lib/libzpool/include/sys/zfs_context.h b/lib/libzpool/include/sys/zfs_context.h
index 5649d4762e..837ddce6ec 100644
--- a/lib/libzpool/include/sys/zfs_context.h
+++ b/lib/libzpool/include/sys/zfs_context.h
@@ -504,6 +504,7 @@ typedef struct callb_cpr {
 #define	zone_dataset_visible(x, y)	(1)
 #define	INGLOBALZONE(z)			(1)
 
+extern char *kmem_vasprintf(const char *fmt, va_list adx);
 extern char *kmem_asprintf(const char *fmt, ...);
 #define	strfree(str) kmem_free((str), strlen(str)+1)
 
diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c
index c7bac38b8f..9d5b1c9547 100644
--- a/lib/libzpool/kernel.c
+++ b/lib/libzpool/kernel.c
@@ -1120,25 +1120,27 @@ ksiddomain_rele(ksiddomain_t *ksid)
 	umem_free(ksid, sizeof (ksiddomain_t));
 }
 
-/*
- * Do not change the length of the returned string; it must be freed
- * with strfree().
- */
+char *
+kmem_vasprintf(const char *fmt, va_list adx)
+{
+	char *buf = NULL;
+	va_list adx_copy;
+
+	va_copy(adx_copy, adx);
+	VERIFY(vasprintf(&buf, fmt, adx_copy) != -1);
+	va_end(adx_copy);
+
+	return (buf);
+}
+
 char *
 kmem_asprintf(const char *fmt, ...)
 {
-	int size;
+	char *buf = NULL;
 	va_list adx;
-	char *buf;
 
 	va_start(adx, fmt);
-	size = vsnprintf(NULL, 0, fmt, adx) + 1;
-	va_end(adx);
-
-	buf = kmem_alloc(size, KM_SLEEP);
-
-	va_start(adx, fmt);
-	size = vsnprintf(buf, size, fmt, adx);
+	VERIFY(vasprintf(&buf, fmt, adx) != -1);
 	va_end(adx);
 
 	return (buf);
diff --git a/module/zfs/spa_history.c b/module/zfs/spa_history.c
index e5ceed9ff6..243f2b4ab3 100644
--- a/module/zfs/spa_history.c
+++ b/module/zfs/spa_history.c
@@ -432,6 +432,7 @@ log_internal(history_internal_events_t event, spa_t *spa,
     dmu_tx_t *tx, const char *fmt, va_list adx)
 {
 	history_arg_t *ha;
+	va_list adx_copy;
 
 	/*
 	 * If this is part of creating a pool, not everything is
@@ -441,7 +442,9 @@ log_internal(history_internal_events_t event, spa_t *spa,
 		return;
 
 	ha = kmem_alloc(sizeof (history_arg_t), KM_SLEEP);
-	ha->ha_history_str = kmem_asprintf(fmt, adx);
+	va_copy(adx_copy, adx);
+	ha->ha_history_str = kmem_vasprintf(fmt, adx_copy);
+	va_end(adx_copy);
 	ha->ha_log_type = LOG_INTERNAL;
 	ha->ha_event = event;
 	ha->ha_zone = NULL;