diff --git a/comma.go b/comma.go
index 3cbd3ca..b65ea6f 100644
--- a/comma.go
+++ b/comma.go
@@ -99,34 +99,3 @@
 	parts[j] = strconv.Itoa(int(b.Int64()))
 	return sign + strings.Join(parts[j:], ",")
 }
-
-// BigCommaf produces a string form of the given big.Float in base 10
-// with commas after every three orders of magnitude.
-func BigCommaf(v *big.Float) string {
-	buf := &bytes.Buffer{}
-	if v.Sign() < 0 {
-		buf.Write([]byte{'-'})
-		v.Abs(v)
-	}
-
-	comma := []byte{','}
-
-	parts := strings.Split(v.Text('f', -1), ".")
-	pos := 0
-	if len(parts[0])%3 != 0 {
-		pos += len(parts[0]) % 3
-		buf.WriteString(parts[0][:pos])
-		buf.Write(comma)
-	}
-	for ; pos < len(parts[0]); pos += 3 {
-		buf.WriteString(parts[0][pos : pos+3])
-		buf.Write(comma)
-	}
-	buf.Truncate(buf.Len() - 1)
-
-	if len(parts) > 1 {
-		buf.Write([]byte{'.'})
-		buf.WriteString(parts[1])
-	}
-	return buf.String()
-}
diff --git a/comma_go15.go b/comma_go15.go
new file mode 100644
index 0000000..9d27cdc
--- /dev/null
+++ b/comma_go15.go
@@ -0,0 +1,40 @@
+// +build go1.5
+
+package humanize
+
+import (
+	"bytes"
+	"math/big"
+	"strings"
+)
+
+// BigCommaf produces a string form of the given big.Float in base 10
+// with commas after every three orders of magnitude.
+func BigCommaf(v *big.Float) string {
+	buf := &bytes.Buffer{}
+	if v.Sign() < 0 {
+		buf.Write([]byte{'-'})
+		v.Abs(v)
+	}
+
+	comma := []byte{','}
+
+	parts := strings.Split(v.Text('f', -1), ".")
+	pos := 0
+	if len(parts[0])%3 != 0 {
+		pos += len(parts[0]) % 3
+		buf.WriteString(parts[0][:pos])
+		buf.Write(comma)
+	}
+	for ; pos < len(parts[0]); pos += 3 {
+		buf.WriteString(parts[0][pos : pos+3])
+		buf.Write(comma)
+	}
+	buf.Truncate(buf.Len() - 1)
+
+	if len(parts) > 1 {
+		buf.Write([]byte{'.'})
+		buf.WriteString(parts[1])
+	}
+	return buf.String()
+}
diff --git a/comma_go15_test.go b/comma_go15_test.go
new file mode 100644
index 0000000..baf777b
--- /dev/null
+++ b/comma_go15_test.go
@@ -0,0 +1,44 @@
+// +build go1.5
+
+package humanize
+
+import (
+	"math"
+	"math/big"
+	"testing"
+)
+
+func BenchmarkBigCommaf(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Commaf(1234567890.83584)
+	}
+}
+
+func TestBigCommafs(t *testing.T) {
+	testList{
+		{"0", BigCommaf(big.NewFloat(0)), "0"},
+		{"10.11", BigCommaf(big.NewFloat(10.11)), "10.11"},
+		{"100", BigCommaf(big.NewFloat(100)), "100"},
+		{"1,000", BigCommaf(big.NewFloat(1000)), "1,000"},
+		{"10,000", BigCommaf(big.NewFloat(10000)), "10,000"},
+		{"100,000", BigCommaf(big.NewFloat(100000)), "100,000"},
+		{"834,142.32", BigCommaf(big.NewFloat(834142.32)), "834,142.32"},
+		{"10,000,000", BigCommaf(big.NewFloat(10000000)), "10,000,000"},
+		{"10,100,000", BigCommaf(big.NewFloat(10100000)), "10,100,000"},
+		{"10,010,000", BigCommaf(big.NewFloat(10010000)), "10,010,000"},
+		{"10,001,000", BigCommaf(big.NewFloat(10001000)), "10,001,000"},
+		{"123,456,789", BigCommaf(big.NewFloat(123456789)), "123,456,789"},
+		{"maxf64", BigCommaf(big.NewFloat(math.MaxFloat64)), "179,769,313,486,231,570,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000"},
+		{"minf64", BigCommaf(big.NewFloat(math.SmallestNonzeroFloat64)), "0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000004940656458412465"},
+		{"-123,456,789", BigCommaf(big.NewFloat(-123456789)), "-123,456,789"},
+		{"-10,100,000", BigCommaf(big.NewFloat(-10100000)), "-10,100,000"},
+		{"-10,010,000", BigCommaf(big.NewFloat(-10010000)), "-10,010,000"},
+		{"-10,001,000", BigCommaf(big.NewFloat(-10001000)), "-10,001,000"},
+		{"-10,000,000", BigCommaf(big.NewFloat(-10000000)), "-10,000,000"},
+		{"-100,000", BigCommaf(big.NewFloat(-100000)), "-100,000"},
+		{"-10,000", BigCommaf(big.NewFloat(-10000)), "-10,000"},
+		{"-1,000", BigCommaf(big.NewFloat(-1000)), "-1,000"},
+		{"-100.11", BigCommaf(big.NewFloat(-100.11)), "-100.11"},
+		{"-10", BigCommaf(big.NewFloat(-10)), "-10"},
+	}.validate(t)
+}
diff --git a/comma_test.go b/comma_test.go
index 734b60d..49040fb 100644
--- a/comma_test.go
+++ b/comma_test.go
@@ -81,12 +81,6 @@
 	}
 }
 
-func BenchmarkBigCommaf(b *testing.B) {
-	for i := 0; i < b.N; i++ {
-		Commaf(1234567890.83584)
-	}
-}
-
 func bigComma(i int64) string {
 	return BigComma(big.NewInt(i))
 }
@@ -138,32 +132,3 @@
 		}
 	}
 }
-
-func TestBigCommafs(t *testing.T) {
-	testList{
-		{"0", BigCommaf(big.NewFloat(0)), "0"},
-		{"10.11", BigCommaf(big.NewFloat(10.11)), "10.11"},
-		{"100", BigCommaf(big.NewFloat(100)), "100"},
-		{"1,000", BigCommaf(big.NewFloat(1000)), "1,000"},
-		{"10,000", BigCommaf(big.NewFloat(10000)), "10,000"},
-		{"100,000", BigCommaf(big.NewFloat(100000)), "100,000"},
-		{"834,142.32", BigCommaf(big.NewFloat(834142.32)), "834,142.32"},
-		{"10,000,000", BigCommaf(big.NewFloat(10000000)), "10,000,000"},
-		{"10,100,000", BigCommaf(big.NewFloat(10100000)), "10,100,000"},
-		{"10,010,000", BigCommaf(big.NewFloat(10010000)), "10,010,000"},
-		{"10,001,000", BigCommaf(big.NewFloat(10001000)), "10,001,000"},
-		{"123,456,789", BigCommaf(big.NewFloat(123456789)), "123,456,789"},
-		{"maxf64", BigCommaf(big.NewFloat(math.MaxFloat64)), "179,769,313,486,231,570,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000"},
-		{"minf64", BigCommaf(big.NewFloat(math.SmallestNonzeroFloat64)), "0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000004940656458412465"},
-		{"-123,456,789", BigCommaf(big.NewFloat(-123456789)), "-123,456,789"},
-		{"-10,100,000", BigCommaf(big.NewFloat(-10100000)), "-10,100,000"},
-		{"-10,010,000", BigCommaf(big.NewFloat(-10010000)), "-10,010,000"},
-		{"-10,001,000", BigCommaf(big.NewFloat(-10001000)), "-10,001,000"},
-		{"-10,000,000", BigCommaf(big.NewFloat(-10000000)), "-10,000,000"},
-		{"-100,000", BigCommaf(big.NewFloat(-100000)), "-100,000"},
-		{"-10,000", BigCommaf(big.NewFloat(-10000)), "-10,000"},
-		{"-1,000", BigCommaf(big.NewFloat(-1000)), "-1,000"},
-		{"-100.11", BigCommaf(big.NewFloat(-100.11)), "-100.11"},
-		{"-10", BigCommaf(big.NewFloat(-10)), "-10"},
-	}.validate(t)
-}