diff --git a/go.mod b/go.mod
index b1f2f0e..93ea3bd 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module github.com/tidwall/geojson
 go 1.15
 
 require (
+	github.com/stretchr/testify v1.8.4
 	github.com/tidwall/gjson v1.12.1
 	github.com/tidwall/lotsa v1.0.2
 	github.com/tidwall/pretty v1.2.0
diff --git a/go.sum b/go.sum
index 541e0cf..db9e2c1 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,15 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
 github.com/tidwall/cities v0.1.0 h1:CVNkmMf7NEC9Bvokf5GoSsArHCKRMTgLuubRTHnH0mE=
 github.com/tidwall/cities v0.1.0/go.mod h1:lV/HDp2gCcRcHJWqgt6Di54GiDrTZwh1aG2ZUPNbqa4=
 github.com/tidwall/geoindex v1.4.4 h1:hdwzy5qNtK75i7nus59Ibr+SwcH4F2v65bw4txrLJ9M=
@@ -14,3 +26,8 @@ github.com/tidwall/rtree v1.3.1 h1:xu3vJPKJrmGce7YJcFUCoqLrp9DTUEJBnVgdPSXHgHs=
 github.com/tidwall/rtree v1.3.1/go.mod h1:S+JSsqPTI8LfWA4xHBo5eXzie8WJLVFeppAutSegl6M=
 github.com/tidwall/sjson v1.2.4 h1:cuiLzLnaMeBhRmEv00Lpk3tkYrcxpmbU81tAY4Dw0tc=
 github.com/tidwall/sjson v1.2.4/go.mod h1:098SZ494YoMWPmMO6ct4dcFnqxwj9r/gF0Etp19pSNM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/object.go b/object.go
index c726ceb..27f777a 100644
--- a/object.go
+++ b/object.go
@@ -258,7 +258,10 @@ func appendJSONPoint(dst []byte, point geometry.Point, ex *extra, idx int) []byt
 		dims := int(ex.dims)
 		for i := 0; i < dims; i++ {
 			dst = append(dst, ',')
-			dst = appendJSONFloat(dst, ex.values[idx*dims+i])
+			k := idx*dims + i
+			if k < len(ex.values) {
+				dst = appendJSONFloat(dst, ex.values[k])
+			}
 		}
 	}
 	dst = append(dst, ']')
diff --git a/object_test.go b/object_test.go
index 1f12c5d..963c6a0 100644
--- a/object_test.go
+++ b/object_test.go
@@ -2,6 +2,7 @@ package geojson
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"math"
 	"math/rand"
@@ -77,7 +78,7 @@ func expectJSONOpts(t testing.TB, data string, expect interface{}, opts *ParseOp
 		exstr = data
 	}
 	obj, err := Parse(data, opts)
-	if err != exerr {
+	if !errors.Is(err, exerr) {
 		if t == nil {
 			panic(fmt.Sprintf("expected '%v', got '%v'", exerr, err))
 		} else {
diff --git a/polygon_test.go b/polygon_test.go
index 3f23f2f..30d9a6e 100644
--- a/polygon_test.go
+++ b/polygon_test.go
@@ -1,6 +1,7 @@
 package geojson
 
 import (
+	"github.com/stretchr/testify/assert"
 	"testing"
 )
 
@@ -76,6 +77,16 @@ func TestEmptyPolygon(t *testing.T) {
 	expect(t, p.JSON() == `{"type":"Polygon","coordinates":[]}`)
 }
 
+func TestPanic(t *testing.T) {
+	p, err := Parse("{\"type\":\"Polygon\",\"coordinates\":[[[0,0],[10,0],[0,10],[0,0]],[[0,0,0],[0,10,0],[10,0,0],[0,0,0]]]}", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := p.String()
+	e := "{\"type\":\"Polygon\",\"coordinates\":[[[0,0],[10,0],[0,10],[0,0]],[[0,0,0],[0,10,0],[10,0,0],[0,0,0]]]}"
+	assert.Equal(t, e, s)
+}
+
 // https://github.com/tidwall/tile38/issues/664
 func TestIssue664(t *testing.T) {
 	// original geojson from issue