diff --git a/parser_test.go b/parser_test.go
index acd9deb..08251e6 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -48,8 +48,8 @@ func TestSlice(t *testing.T) {
 	}))
 	t.Run("fails at end of input", rapid.MakeCheck(func(t *rapid.T) {
 		s := rapid.SliceOfN(rapid.Byte(), 1, -1).Draw(t, "s")
-		inputLen := rapid.IntRange(0, len(s)-1).Draw(t, "inputLen")
-		input := s[:inputLen]
+		input := rapid.Map(rapid.IntRange(0, len(s)-1),
+			func(n int) []byte { return s[:n] }).Draw(t, "inputLen")
 		assertParseFails(t, input, gigaparsec.MatchSlice(s))
 	}))
 	t.Run("fails when read fails", rapid.MakeCheck(func(t *rapid.T) {
@@ -63,8 +63,8 @@ func TestSlice(t *testing.T) {
 	}))
 	t.Run("succeeds when contents match", rapid.MakeCheck(func(t *rapid.T) {
 		input := rapid.SliceOfN(rapid.Byte(), 1, -1).Draw(t, "input")
-		sLen := rapid.IntRange(0, len(input)).Draw(t, "sLen")
-		s := input[:sLen]
+		s := rapid.Map(rapid.IntRange(0, len(input)),
+			func(n int) []byte { return input[:n] }).Draw(t, "s")
 		start := gigaparsec.MakeState(bytes.NewReader(input))
 
 		result, err := gigaparsec.MatchSlice(s)(start)