diff --git a/.github/workflows/unit_test.yml b/.github/workflows/unit_test.yml
index eb36d76..cbadf39 100644
--- a/.github/workflows/unit_test.yml
+++ b/.github/workflows/unit_test.yml
@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: [ '1.15', '1.16', '1.17' ]
+        go: [ '1.18', '1.19' ]
     name: Go ${{ matrix.go }} test
     steps:
       - uses: actions/checkout@v2
diff --git a/README.md b/README.md
index 3026435..1512a29 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 go-iap
 ======
 
-![](https://img.shields.io/badge/golang-1.15+-blue.svg?style=flat)
+![](https://img.shields.io/badge/golang-1.18+-blue.svg?style=flat)
 [![Build Status](https://travis-ci.org/awa/go-iap.svg?branch=master)](https://travis-ci.org/awa/go-iap)
 [![codecov.io](https://codecov.io/github/awa/go-iap/coverage.svg?branch=master)](https://codecov.io/github/awa/go-iap?branch=master)
 
diff --git a/amazon/validator_test.go b/amazon/validator_test.go
index d5d2b0c..ea9c216 100644
--- a/amazon/validator_test.go
+++ b/amazon/validator_test.go
@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
-	"net/url"
 	"os"
 	"reflect"
 	"testing"
@@ -169,21 +168,16 @@ func TestVerifyEntitled(t *testing.T) {
 
 func TestVerifyTimeout(t *testing.T) {
 	t.Parallel()
-	// HTTP 100 is "continue" so it will time out
-	server, client := testTools(100, "timeout response")
+	server, client := testTools(http.StatusGatewayTimeout, "{\"message\": \"timeout response\"}")
 	defer server.Close()
 
 	ctx := context.Background()
 	_, actual := client.Verify(ctx, "timeout", "timeout")
-
-	// Actual should be a "request canceled" *url.Error
-	urlErr, ok := actual.(*url.Error)
-	if !ok {
-		t.Errorf("Expected *url.Error, got %T", actual)
+	if actual == nil {
+		t.Error("expected error, got nil")
 	}
-
-	if !urlErr.Timeout() {
-		t.Errorf("got %v\nwant timeout", actual)
+	if actual.Error() != "timeout response" {
+		t.Errorf("got %v\nwant %v", actual, "timeout response")
 	}
 }
 
diff --git a/go.mod b/go.mod
index eaf74fc..abba7ef 100644
--- a/go.mod
+++ b/go.mod
@@ -1,17 +1,26 @@
 module github.com/awa/go-iap
 
-go 1.15
+go 1.18
 
 require (
 	github.com/golang-jwt/jwt/v4 v4.3.0
-	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
 	github.com/golang/mock v1.5.0
 	github.com/google/uuid v1.3.0
-	golang.org/x/net v0.0.0-20211015210444-4f30a5c0130f // indirect
 	golang.org/x/oauth2 v0.0.0-20210514164344-f6687ab2804c
-	golang.org/x/sys v0.0.0-20211019181941-9d821ace8654 // indirect
-	golang.org/x/text v0.3.7 // indirect
 	google.golang.org/api v0.48.0
 	google.golang.org/appengine v1.6.7
+)
+
+require (
+	cloud.google.com/go v0.83.0 // indirect
+	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/googleapis/gax-go/v2 v2.0.5 // indirect
+	go.opencensus.io v0.23.0 // indirect
+	golang.org/x/net v0.0.0-20211015210444-4f30a5c0130f // indirect
+	golang.org/x/sys v0.0.0-20211019181941-9d821ace8654 // indirect
+	golang.org/x/text v0.3.7 // indirect
 	google.golang.org/genproto v0.0.0-20210607140030-00d4fb20b1ae // indirect
+	google.golang.org/grpc v1.38.0 // indirect
+	google.golang.org/protobuf v1.26.0 // indirect
 )