diff --git a/CHANGELOG b/CHANGELOG
index 153dfeb..3e48ece 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,6 +6,7 @@ Bug fixes:
 - Don't fail adding a feed which collides with another via redirection
 - Don't fail on very long text-search queries containing question marks
   when using PostgreSQL or MySQL
+- Specify HTTP authentication encoding as UTF-8
 
 Changes:
 - Include a user manual
diff --git a/lib/REST.php b/lib/REST.php
index 989205f..9212326 100644
--- a/lib/REST.php
+++ b/lib/REST.php
@@ -150,7 +150,7 @@ class REST {
 
     public function challenge(ResponseInterface $res, string $realm = null): ResponseInterface {
         $realm = $realm ?? Arsse::$conf->httpRealm;
-        return $res->withAddedHeader("WWW-Authenticate", 'Basic realm="'.$realm.'"');
+        return $res->withAddedHeader("WWW-Authenticate", 'Basic realm="'.$realm.'", charset="UTF-8"');
     }
 
     public function normalizeResponse(ResponseInterface $res, RequestInterface $req = null): ResponseInterface {
diff --git a/tests/cases/REST/TestREST.php b/tests/cases/REST/TestREST.php
index 994d6ac..fb0dc2f 100644
--- a/tests/cases/REST/TestREST.php
+++ b/tests/cases/REST/TestREST.php
@@ -97,10 +97,10 @@ class TestREST extends \JKingWeb\Arsse\Test\AbstractTest {
         self::setConf();
         $r = new REST();
         $in = new EmptyResponse(401);
-        $exp = $in->withHeader("WWW-Authenticate", 'Basic realm="OOK"');
+        $exp = $in->withHeader("WWW-Authenticate", 'Basic realm="OOK", charset="UTF-8"');
         $act = $r->challenge($in, "OOK");
         $this->assertMessage($exp, $act);
-        $exp = $in->withHeader("WWW-Authenticate", 'Basic realm="'.Arsse::$conf->httpRealm.'"');
+        $exp = $in->withHeader("WWW-Authenticate", 'Basic realm="'.Arsse::$conf->httpRealm.'", charset="UTF-8"');
         $act = $r->challenge($in);
         $this->assertMessage($exp, $act);
     }