diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index faeb019120658d538bb3de18f9c41c668f14837e..d3bccf4ddb7f7c631b321da111242e758fa6ada9 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -520,8 +520,9 @@ (define (cache-entry cache-uri narinfo)
 (define (narinfo-request cache-url path)
   "Return an HTTP request for the narinfo of PATH at CACHE-URL."
   (let ((url (string-append cache-url "/" (store-path-hash-part path)
-                            ".narinfo")))
-    (build-request (string->uri url) #:method 'GET)))
+                            ".narinfo"))
+        (headers '((User-Agent . "GNU Guile"))))
+    (build-request (string->uri url) #:method 'GET #:headers headers)))
 
 (define* (http-multiple-get base-uri proc seed requests
                             #:key port (verify-certificate? #t))