diff --git a/command.go b/command.go
index f21e2db..7f49b78 100644
--- a/command.go
+++ b/command.go
@@ -18,8 +18,8 @@ type Cmder interface {
 	Args() []interface{}
 	String() string
 	stringArg(int) string
-	firstKeyPos() int
-	addKeyPos(int)
+	firstKeyPos() int8
+	setFirstKeyPos(int8)
 
 	readTimeout() *time.Duration
 	readReply(rd *proto.Reader) error
@@ -59,6 +59,10 @@ func writeCmd(wr *proto.Writer, cmd Cmder) error {
 }
 
 func cmdFirstKeyPos(cmd Cmder, info *CommandInfo) int {
+	if pos := cmd.firstKeyPos(); pos != 0 {
+		return int(pos)
+	}
+
 	switch cmd.Name() {
 	case "eval", "evalsha":
 		if cmd.stringArg(2) != "0" {
@@ -75,13 +79,10 @@ func cmdFirstKeyPos(cmd Cmder, info *CommandInfo) int {
 		}
 	}
 
-	if pos := cmd.firstKeyPos(); pos != 0 {
-		return pos
+	if info != nil {
+		return int(info.FirstKeyPos)
 	}
-	if info == nil {
-		return 0
-	}
-	return int(info.FirstKeyPos)
+	return 0
 }
 
 func cmdString(cmd Cmder, val interface{}) string {
@@ -108,10 +109,10 @@ func cmdString(cmd Cmder, val interface{}) string {
 //------------------------------------------------------------------------------
 
 type baseCmd struct {
-	ctx  context.Context
-	args []interface{}
-	err  error
-	keyPos int
+	ctx    context.Context
+	args   []interface{}
+	err    error
+	keyPos int8
 
 	_readTimeout *time.Duration
 }
@@ -153,12 +154,12 @@ func (cmd *baseCmd) stringArg(pos int) string {
 	return s
 }
 
-func (cmd *baseCmd) firstKeyPos() int {
+func (cmd *baseCmd) firstKeyPos() int8 {
 	return cmd.keyPos
 }
 
-func (cmd *baseCmd) addKeyPos(offset int)  {
-	cmd.keyPos += offset
+func (cmd *baseCmd) setFirstKeyPos(keyPos int8) {
+	cmd.keyPos = keyPos
 }
 
 func (cmd *baseCmd) SetErr(e error) {
diff --git a/commands.go b/commands.go
index e70eac4..a6c9eee 100644
--- a/commands.go
+++ b/commands.go
@@ -1505,19 +1505,19 @@ func (c cmdable) XRead(ctx context.Context, a *XReadArgs) *XStreamSliceCmd {
 	args := make([]interface{}, 0, 5+len(a.Streams))
 	args = append(args, "xread")
 
-	offset := 1
+	keyPos := int8(1)
 	if a.Count > 0 {
 		args = append(args, "count")
 		args = append(args, a.Count)
-		offset += 2
+		keyPos += 2
 	}
 	if a.Block >= 0 {
 		args = append(args, "block")
 		args = append(args, int64(a.Block/time.Millisecond))
-		offset += 2
+		keyPos += 2
 	}
 	args = append(args, "streams")
-	offset += 1
+	keyPos += 1
 	for _, s := range a.Streams {
 		args = append(args, s)
 	}
@@ -1526,7 +1526,7 @@ func (c cmdable) XRead(ctx context.Context, a *XReadArgs) *XStreamSliceCmd {
 	if a.Block >= 0 {
 		cmd.setReadTimeout(a.Block)
 	}
-	cmd.addKeyPos(offset)
+	cmd.setFirstKeyPos(keyPos)
 	_ = c(ctx, cmd)
 	return cmd
 }
@@ -1581,21 +1581,21 @@ func (c cmdable) XReadGroup(ctx context.Context, a *XReadGroupArgs) *XStreamSlic
 	args := make([]interface{}, 0, 8+len(a.Streams))
 	args = append(args, "xreadgroup", "group", a.Group, a.Consumer)
 
-	offset := 1
+	keyPos := int8(1)
 	if a.Count > 0 {
 		args = append(args, "count", a.Count)
-		offset += 2
+		keyPos += 2
 	}
 	if a.Block >= 0 {
 		args = append(args, "block", int64(a.Block/time.Millisecond))
-		offset += 2
+		keyPos += 2
 	}
 	if a.NoAck {
 		args = append(args, "noack")
-		offset += 1
+		keyPos += 1
 	}
 	args = append(args, "streams")
-	offset += 1
+	keyPos += 1
 	for _, s := range a.Streams {
 		args = append(args, s)
 	}
@@ -1604,7 +1604,7 @@ func (c cmdable) XReadGroup(ctx context.Context, a *XReadGroupArgs) *XStreamSlic
 	if a.Block >= 0 {
 		cmd.setReadTimeout(a.Block)
 	}
-	cmd.addKeyPos(offset)
+	cmd.setFirstKeyPos(keyPos)
 	_ = c(ctx, cmd)
 	return cmd
 }
@@ -1883,7 +1883,7 @@ func (c cmdable) ZInterStore(ctx context.Context, destination string, store *ZSt
 		args = append(args, "aggregate", store.Aggregate)
 	}
 	cmd := NewIntCmd(ctx, args...)
-	cmd.addKeyPos(3)
+	cmd.setFirstKeyPos(3)
 	_ = c(ctx, cmd)
 	return cmd
 }
@@ -2118,8 +2118,9 @@ func (c cmdable) ZUnionStore(ctx context.Context, dest string, store *ZStore) *I
 	if store.Aggregate != "" {
 		args = append(args, "aggregate", store.Aggregate)
 	}
+
 	cmd := NewIntCmd(ctx, args...)
-	cmd.addKeyPos(3)
+	cmd.setFirstKeyPos(3)
 	_ = c(ctx, cmd)
 	return cmd
 }