diff --git a/keccak.go b/keccak.go
index d0a12ca..dfa0a8e 100644
--- a/keccak.go
+++ b/keccak.go
@@ -1,10 +1,10 @@
 package keccak
 
 // roundGeneric implements one round of the keccak-f[1600] permutation.
-func roundGeneric(a [5][5]uint64) [5][5]uint64 {
+func roundGeneric(a *[5][5]uint64) {
 	// Theta
 	var c [5]uint64
-	for x := range a {
+	for x := range *a {
 		c[x] = a[0][x] ^ a[1][x] ^ a[2][x] ^ a[3][x] ^ a[4][x]
 	}
 	for x := range a[0] {
@@ -18,7 +18,7 @@ func roundGeneric(a [5][5]uint64) [5][5]uint64 {
 
 	// Rho and pi
 	var b [5][5]uint64
-	for y := range a {
+	for y := range *a {
 		for x := range a[0] {
 			x0 := y
 			y0 := (x*2 + y*3) % 5
@@ -35,8 +35,6 @@ func roundGeneric(a [5][5]uint64) [5][5]uint64 {
 		a[y][3] = b[y][3] ^ ^c[4] & c[0]
 		a[y][4] = b[y][4] ^ ^c[0] & c[1]
 	}
-
-	return a
 }
 
 
diff --git a/sponge.go b/sponge.go
index 114f91f..1fb74ca 100644
--- a/sponge.go
+++ b/sponge.go
@@ -49,16 +49,15 @@ loop:
 			b = b[8:]
 		}
 	}
-	d.a = keccakf(d.a)
+	keccakf(&d.a)
 	d.len = 0
 }
 
-func keccakf(a [5][5]uint64) [5][5]uint64 {
+func keccakf(a *[5][5]uint64) {
 	for i := 0; i < 24; i++ {
-		a = roundGeneric(a)
+		roundGeneric(a)
 		a[0][0] ^= RC[i]
 	}
-	return a
 }
 
 func (d0 *digest) Sum(b []byte) []byte {