diff --git a/src/pkg/math/rand/rand.go b/src/pkg/math/rand/rand.go
index 2157cdb465..04fb67d19d 100644
--- a/src/pkg/math/rand/rand.go
+++ b/src/pkg/math/rand/rand.go
@@ -103,12 +103,10 @@ func (r *Rand) Float32() float32 { return float32(r.Float64()) }
 // Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).
 func (r *Rand) Perm(n int) []int {
 	m := make([]int, n)
-	for i := 0; i < n; i++ {
-		m[i] = i
-	}
 	for i := 0; i < n; i++ {
 		j := r.Intn(i + 1)
-		m[i], m[j] = m[j], m[i]
+		m[i] = m[j]
+		m[j] = i
 	}
 	return m
 }
diff --git a/src/pkg/math/rand/rand_test.go b/src/pkg/math/rand/rand_test.go
index 4d3abdb606..4f0a8d0ee9 100644
--- a/src/pkg/math/rand/rand_test.go
+++ b/src/pkg/math/rand/rand_test.go
@@ -357,3 +357,17 @@ func BenchmarkInt31n1000(b *testing.B) {
 		r.Int31n(1000)
 	}
 }
+
+func BenchmarkPerm3(b *testing.B) {
+	r := New(NewSource(1))
+	for n := b.N; n > 0; n-- {
+		r.Perm(3)
+	}
+}
+
+func BenchmarkPerm30(b *testing.B) {
+	r := New(NewSource(1))
+	for n := b.N; n > 0; n-- {
+		r.Perm(30)
+	}
+}