diff --git a/qb/select.go b/qb/select.go
index bc6ed74..73fed17 100644
--- a/qb/select.go
+++ b/qb/select.go
@@ -10,7 +10,6 @@ package qb
 import (
 	"bytes"
 	"fmt"
-	"strings"
 )
 
 // Order specifies sorting order.
@@ -54,7 +53,11 @@ func (b *SelectBuilder) ToCql() (stmt string, names []string) {
 		cql.WriteString("DISTINCT ")
 		b.distinct.writeCql(&cql)
 	case len(b.groupBy) > 0:
-		cql.WriteString(strings.Join(append(b.groupBy, b.columns...), ","))
+		b.groupBy.writeCql(&cql)
+		if len(b.columns) != 0 {
+			cql.WriteByte(',')
+			b.columns.writeCql(&cql)
+		}
 	case len(b.columns) == 0:
 		cql.WriteByte('*')
 	default:
diff --git a/qb/utils.go b/qb/utils.go
index 8b78b2b..ffa4ab4 100644
--- a/qb/utils.go
+++ b/qb/utils.go
@@ -6,7 +6,6 @@ package qb
 
 import (
 	"bytes"
-	"strings"
 )
 
 // placeholders returns a string with count ? placeholders joined with commas.
@@ -25,5 +24,10 @@ func placeholders(cql *bytes.Buffer, count int) {
 type columns []string
 
 func (cols columns) writeCql(cql *bytes.Buffer) {
-	cql.WriteString(strings.Join(cols, ","))
+	for i, c := range cols {
+		cql.WriteString(c)
+		if i < len(cols)-1 {
+			cql.WriteByte(',')
+		}
+	}
 }