diff --git a/lib/SimpleSAML/Utils/HTTP.php b/lib/SimpleSAML/Utils/HTTP.php
index ef9b4784ab2fb7ffb02a11962b13c949df67ea1e..c839f4efdda71518382b60cd24e6e4b97675e889 100644
--- a/lib/SimpleSAML/Utils/HTTP.php
+++ b/lib/SimpleSAML/Utils/HTTP.php
@@ -417,7 +417,7 @@ class HTTP
             }
             $proxy_auth = $config->getString('proxy.auth', false);
             if ($proxy_auth !== false) {
-                $context['http']['header'] = "Proxy-Authorization: Basic".base64_encode($proxy_auth);
+                $context['http']['header'] = "Proxy-Authorization: Basic ".base64_encode($proxy_auth);
             }
             if (!isset($context['http']['request_fulluri'])) {
                 $context['http']['request_fulluri'] = true;