diff --git a/Makefile b/Makefile
index d3763d6..1107e5f 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,7 @@ testdeps: .test/redis/src/redis-server
 
 .test/redis:
 	mkdir -p $@
-	wget -qO- https://github.com/antirez/redis/archive/3.0.tar.gz | tar xvz --strip-components=1 -C $@
+	wget -qO- https://github.com/antirez/redis/archive/3.0.3.tar.gz | tar xvz --strip-components=1 -C $@
 
 .test/redis/src/redis-server: .test/redis
 	cd $< && make all
diff --git a/commands.go b/commands.go
index 7f10a2f..887fd73 100644
--- a/commands.go
+++ b/commands.go
@@ -526,6 +526,9 @@ func (c *commandable) MSetNX(pairs ...string) *BoolCmd {
 	return cmd
 }
 
+// Redis `SET key value [expiration]` command.
+//
+// Zero expiration means the key has no expiration time.
 func (c *commandable) Set(key string, value interface{}, expiration time.Duration) *StatusCmd {
 	args := make([]interface{}, 3, 5)
 	args[0] = "SET"
@@ -554,6 +557,9 @@ func (c *commandable) SetBit(key string, offset int64, value int) *IntCmd {
 	return cmd
 }
 
+// Redis `SET key value [expiration] NX` command.
+//
+// Zero expiration means the key has no expiration time.
 func (c *commandable) SetNX(key string, value interface{}, expiration time.Duration) *BoolCmd {
 	var cmd *BoolCmd
 	if expiration == 0 {
@@ -570,6 +576,9 @@ func (c *commandable) SetNX(key string, value interface{}, expiration time.Durat
 	return cmd
 }
 
+// Redis `SET key value [expiration] XX` command.
+//
+// Zero expiration means the key has no expiration time.
 func (c *Client) SetXX(key string, value interface{}, expiration time.Duration) *BoolCmd {
 	var cmd *BoolCmd
 	if usePrecise(expiration) {
diff --git a/example_test.go b/example_test.go
index 25869be..de9f8da 100644
--- a/example_test.go
+++ b/example_test.go
@@ -84,6 +84,21 @@ func ExampleClient() {
 	// key2 does not exists
 }
 
+func ExampleClient_Set() {
+	// Last argument is expiration. Zero means the key has no
+	// expiration time.
+	err := client.Set("key", "value", 0).Err()
+	if err != nil {
+		panic(err)
+	}
+
+	// key2 will expire in an hour.
+	err = client.Set("key2", "value", time.Hour).Err()
+	if err != nil {
+		panic(err)
+	}
+}
+
 func ExampleClient_Incr() {
 	if err := client.Incr("counter").Err(); err != nil {
 		panic(err)