diff --git a/oauthex/resource_meta.go b/oauthex/resource_meta.go
index 2869c82f..b71371f4 100644
--- a/oauthex/resource_meta.go
+++ b/oauthex/resource_meta.go
@@ -110,6 +110,7 @@ type Challenge struct {
 	Scheme string
 	// Params is a map of authentication parameters.
 	// Keys are case-insensitive. Parsed keys are always lower-case.
+	// A challenge that carries a token68 instead of parameters has no Params.
 	Params map[string]string
 }
 
@@ -255,6 +256,11 @@ func parseSingleChallenge(s string) (Challenge, error) {
 	if !found {
 		return c, nil
 	}
+	if isToken68(strings.TrimSpace(paramsStr)) {
+		// The challenge carries a token68 (for example, Negotiate with a
+		// SPNEGO token) rather than auth-params. It has no parameters.
+		return c, nil
+	}
 
 	params := make(map[string]string)
 	paramsStr = trimEmptyListElements(paramsStr)
@@ -339,3 +345,22 @@ func trimEmptyListElements(s string) string {
 		return r == ',' || unicode.IsSpace(r)
 	})
 }
+
+// isToken68 reports whether s is a token68 (RFC 9110, section 11.2):
+//
+//	token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" ) *"="
+func isToken68(s string) bool {
+	body := strings.TrimRight(s, "=")
+	if body == "" {
+		return false
+	}
+	for _, r := range body {
+		switch {
+		case 'a' <= r && r <= 'z', 'A' <= r && r <= 'Z', '0' <= r && r <= '9':
+		case strings.ContainsRune("-._~+/", r):
+		default:
+			return false
+		}
+	}
+	return true
+}
diff --git a/oauthex/resource_meta_test.go b/oauthex/resource_meta_test.go
index c6678006..d50626fa 100644
--- a/oauthex/resource_meta_test.go
+++ b/oauthex/resource_meta_test.go
@@ -198,6 +198,27 @@ func TestParseWWWAuthenticateEmptyListElements(t *testing.T) {
 	}
 }
 
+// A challenge may carry a token68 instead of auth-params (RFC 9110,
+// section 11.6.1). It must not stop the Bearer challenge next to it from
+// being parsed.
+func TestParseWWWAuthenticateToken68(t *testing.T) {
+	got, err := ParseWWWAuthenticate([]string{
+		`Negotiate oYH1MIHyoAMKAQ, Bearer resource_metadata="https://example.com/.well-known/oauth-protected-resource"`,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []Challenge{
+		{Scheme: "negotiate"},
+		{Scheme: "bearer", Params: map[string]string{
+			"resource_metadata": "https://example.com/.well-known/oauth-protected-resource",
+		}},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("ParseWWWAuthenticate() = %+v, want %+v", got, want)
+	}
+}
+
 func TestSplitChallengesError(t *testing.T) {
 	if _, err := splitChallenges(`"Bearer"`); err == nil {
 		t.Fatal("got nil, want error")
@@ -300,8 +321,18 @@ func TestParseSingleChallenge(t *testing.T) {
 			wantErr: false,
 		},
 		{
-			name:    "malformed param - no value",
-			input:   "Bearer realm=",
+			name:  "token68",
+			input: "Negotiate oYH1MIHyoAMKAQ",
+			want:  Challenge{Scheme: "negotiate"},
+		},
+		{
+			name:  "token68 with padding",
+			input: "Basic dGVzdA==",
+			want:  Challenge{Scheme: "basic"},
+		},
+		{
+			name:    "malformed token68",
+			input:   "Negotiate abc def",
 			wantErr: true,
 		},
 		{