diff --git a/pkg/eval/vals/assoc_test.go b/pkg/eval/vals/assoc_test.go
index e0718a53..5f92f147 100644
--- a/pkg/eval/vals/assoc_test.go
+++ b/pkg/eval/vals/assoc_test.go
@@ -29,7 +29,7 @@ func TestAssoc(t *testing.T) {
 			Eq(MakeList("foo", "1", "2", "3")), nil),
 		Args(MakeList("0"), MakeList("0"), "1").Rets(nil, errIndexMustBeInteger),
 		Args(MakeList("0"), "1", "x").Rets(nil, errs.OutOfRange{
-			What: "index here", ValidLow: "0", ValidHigh: "0", Actual: "1"}),
+			What: "index", ValidLow: "0", ValidHigh: "0", Actual: "1"}),
 		// TODO: Support list assoc with slice
 		Args(MakeList("0", "1", "2", "3"), "1:3", MakeList("foo")).Rets(
 			nil, errAssocWithSlice),
diff --git a/pkg/eval/vals/index_list.go b/pkg/eval/vals/index_list.go
index 4eda7673..f75c0166 100644
--- a/pkg/eval/vals/index_list.go
+++ b/pkg/eval/vals/index_list.go
@@ -84,12 +84,12 @@ func ConvertListIndex(rawIndex interface{}, n int) (*ListIndex, error) {
 			if j < i {
 				if j0 < 0 {
 					return nil, errs.OutOfRange{
-						What:     "negative slice upper index here",
+						What:     "negative slice upper index",
 						ValidLow: strconv.Itoa(i - n), ValidHigh: "-1",
 						Actual: strconv.Itoa(j0)}
 				}
 				return nil, errs.OutOfRange{
-					What:     "slice upper index here",
+					What:     "slice upper index",
 					ValidLow: strconv.Itoa(i), ValidHigh: strconv.Itoa(n),
 					Actual: strconv.Itoa(j0)}
 			}
@@ -115,7 +115,7 @@ func parseIndexString(s string, n int) (slice bool, i int, j int, err error) {
 	if low == "" {
 		i = 0
 	} else {
-		i, err = atoi(low, n)
+		i, err = atoi(low, n+1)
 		if err != nil {
 			return false, 0, 0, err
 		}
@@ -123,11 +123,12 @@ func parseIndexString(s string, n int) (slice bool, i int, j int, err error) {
 	if high == "" {
 		j = n
 	} else {
-		j, err = atoi(high, n)
+		j, err = atoi(high, n+1)
 		if err != nil {
 			return false, 0, 0, err
 		}
 		if sep == "..=" {
+			// TODO: Handle j == MaxInt-1
 			j++
 		}
 	}
@@ -166,12 +167,12 @@ func atoi(a string, n int) (int, error) {
 
 func posIndexOutOfRange(index string, n int) errs.OutOfRange {
 	return errs.OutOfRange{
-		What:     "index here",
+		What:     "index",
 		ValidLow: "0", ValidHigh: strconv.Itoa(n - 1), Actual: index}
 }
 
 func negIndexOutOfRange(index string, n int) errs.OutOfRange {
 	return errs.OutOfRange{
-		What:     "negative index here",
+		What:     "negative index",
 		ValidLow: strconv.Itoa(-n), ValidHigh: "-1", Actual: index}
 }
diff --git a/pkg/eval/vals/index_test.go b/pkg/eval/vals/index_test.go
index 71d9fc05..db2cf5eb 100644
--- a/pkg/eval/vals/index_test.go
+++ b/pkg/eval/vals/index_test.go
@@ -46,16 +46,20 @@ func TestIndex(t *testing.T) {
 		Args(li4, "0").Rets("foo", nil),
 		Args(li4, "3").Rets("ipsum", nil),
 		Args(li0, "0").Rets(Any, errs.OutOfRange{
-			What: "index here", ValidLow: "0", ValidHigh: "-1", Actual: "0"}),
+			What: "index", ValidLow: "0", ValidHigh: "-1", Actual: "0"}),
 		Args(li4, "4").Rets(Any, errs.OutOfRange{
-			What: "index here", ValidLow: "0", ValidHigh: "3", Actual: "4"}),
+			What: "index", ValidLow: "0", ValidHigh: "3", Actual: "4"}),
 		Args(li4, "5").Rets(Any, errs.OutOfRange{
-			What: "index here", ValidLow: "0", ValidHigh: "3", Actual: "5"}),
+			What: "index", ValidLow: "0", ValidHigh: "3", Actual: "5"}),
+		Args(li4, z).Rets(Any,
+			errs.OutOfRange{What: "index", ValidLow: "0", ValidHigh: "3", Actual: z}),
 		// Negative indices: -n <= i < 0.
 		Args(li4, "-1").Rets("ipsum", nil),
 		Args(li4, "-4").Rets("foo", nil),
 		Args(li4, "-5").Rets(Any, errs.OutOfRange{
-			What: "negative index here", ValidLow: "-4", ValidHigh: "-1", Actual: "-5"}),
+			What: "negative index", ValidLow: "-4", ValidHigh: "-1", Actual: "-5"}),
+		Args(li4, "-"+z).Rets(Any,
+			errs.OutOfRange{What: "negative index", ValidLow: "-4", ValidHigh: "-1", Actual: "-" + z}),
 		// Float indices are not allowed even if the value is an integer.
 		Args(li4, 0.0).Rets(Any, errIndexMustBeInteger),
 
@@ -63,10 +67,10 @@ func TestIndex(t *testing.T) {
 		Args(li4, 0).Rets("foo", nil),
 		Args(li4, 3).Rets("ipsum", nil),
 		Args(li4, 5).Rets(nil, errs.OutOfRange{
-			What: "index here", ValidLow: "0", ValidHigh: "3", Actual: "5"}),
+			What: "index", ValidLow: "0", ValidHigh: "3", Actual: "5"}),
 		Args(li4, -1).Rets("ipsum", nil),
 		Args(li4, -5).Rets(nil, errs.OutOfRange{
-			What: "negative index here", ValidLow: "-4", ValidHigh: "-1", Actual: "-5"}),
+			What: "negative index", ValidLow: "-4", ValidHigh: "-1", Actual: "-5"}),
 
 		// Half-open slices.
 		Args(li4, "1..3").Rets(Eq(MakeList("bar", "lorem")), nil),
@@ -102,13 +106,19 @@ func TestIndex(t *testing.T) {
 		Args(li4, "3..=").Rets(Eq(MakeList("ipsum")), nil),
 		Args(li4, "..=").Rets(Eq(li4), nil),
 
-		// Index out of range.
+		// Slice index out of range.
 		Args(li4, "-5:1").Rets(nil, errs.OutOfRange{
-			What: "negative index here", ValidLow: "-4", ValidHigh: "-1", Actual: "-5"}),
+			What: "negative index", ValidLow: "-4", ValidHigh: "-1", Actual: "-5"}),
 		Args(li4, "0:5").Rets(nil, errs.OutOfRange{
-			What: "index here", ValidLow: "0", ValidHigh: "4", Actual: "5"}),
+			What: "index", ValidLow: "0", ValidHigh: "4", Actual: "5"}),
+		Args(li4, z+":").Rets(nil,
+			errs.OutOfRange{What: "index", ValidLow: "0", ValidHigh: "4", Actual: z}),
+		// Slice index upper < lower
 		Args(li4, "3:2").Rets(nil, errs.OutOfRange{
-			What: "slice upper index here", ValidLow: "3", ValidHigh: "4", Actual: "2"}),
+			What: "slice upper index", ValidLow: "3", ValidHigh: "4", Actual: "2"}),
+		Args(li4, "-1:-2").Rets(nil,
+			errs.OutOfRange{What: "negative slice upper index",
+				ValidLow: "-1", ValidHigh: "-1", Actual: "-2"}),
 
 		// Malformed list indices.
 		Args(li4, "a").Rets(Any, errIndexMustBeInteger),