diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2272fb4..fc41907 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -100,6 +100,7 @@
 - [#750](https://github.com/oauth2-proxy/oauth2-proxy/pull/750) ci: Migrate to Github Actions (@shinebayar-g)
 - [#829](https://github.com/oauth2-proxy/oauth2-proxy/pull/820) Rename test directory to testdata (@johejo)
 - [#819](https://github.com/oauth2-proxy/oauth2-proxy/pull/819) Improve CI (@johejo)
+- [#989](https://github.com/oauth2-proxy/oauth2-proxy/pull/989) Adapt isAjax to support mimetype lists (@rassie)
 
 # v6.1.1
 
diff --git a/oauthproxy.go b/oauthproxy.go
index 74ed6dc..cfba693 100644
--- a/oauthproxy.go
+++ b/oauthproxy.go
@@ -1111,9 +1111,17 @@ func (p *OAuthProxy) addHeadersForProxying(rw http.ResponseWriter, req *http.Req
 func isAjax(req *http.Request) bool {
 	acceptValues := req.Header.Values("Accept")
 	const ajaxReq = applicationJSON
-	for _, v := range acceptValues {
-		if v == ajaxReq {
-			return true
+	// Iterate over multiple Accept headers, i.e.
+	// Accept: application/json
+	// Accept: text/plain
+	for _, mimeTypes := range acceptValues {
+		// Iterate over multiple mimetypes in a single header, i.e.
+		// Accept: application/json, text/plain, */*
+		for _, mimeType := range strings.Split(mimeTypes, ",") {
+			mimeType = strings.TrimSpace(mimeType)
+			if mimeType == ajaxReq {
+				return true
+			}
 		}
 	}
 	return false
diff --git a/oauthproxy_test.go b/oauthproxy_test.go
index 572e1ec..52ffa2b 100644
--- a/oauthproxy_test.go
+++ b/oauthproxy_test.go
@@ -1970,6 +1970,13 @@ func TestAjaxUnauthorizedRequest2(t *testing.T) {
 	testAjaxUnauthorizedRequest(t, header)
 }
 
+func TestAjaxUnauthorizedRequestAccept1(t *testing.T) {
+	header := make(http.Header)
+	header.Add("Accept", "application/json, text/plain, */*")
+
+	testAjaxUnauthorizedRequest(t, header)
+}
+
 func TestAjaxForbiddendRequest(t *testing.T) {
 	test, err := newAjaxRequestTest()
 	if err != nil {