diff --git a/src/device/input/random.go b/src/device/input/random.go
index c487002..3039054 100644
--- a/src/device/input/random.go
+++ b/src/device/input/random.go
@@ -6,6 +6,7 @@ import (
 	"io"
 	"math/rand"
 	"os"
+	"sort"
 	"time"
 
 	"github.com/go-yaml/yaml"
@@ -87,11 +88,15 @@ func randomCharFromWeights(m map[byte]int) func() byte {
 		}
 		sum += v
 	}
+	sort.Slice(result, func(i, j int) bool {
+		return result[i].i < result[j].i
+	})
 	if sum <= 0 {
 		panic("weights must total nonzero")
 	}
 	return func() byte {
-		n := rand.Int() % sum
+		r := rand.Int()
+		n := r % (sum + 1)
 		for _, v := range result {
 			n -= v.i
 			if n <= 0 {
diff --git a/src/device/input/random_test.go b/src/device/input/random_test.go
index df0812e..91feeeb 100644
--- a/src/device/input/random_test.go
+++ b/src/device/input/random_test.go
@@ -8,7 +8,7 @@ import (
 func TestRandomCharFromWeights(t *testing.T) {
 	weights := map[byte]int{
 		'a': 1,
-		'b': 99,
+		'b': 20,
 	}
 	foo := randomCharFromWeights(weights)
 	for {