diff --git a/guix-data-service/web/render.scm b/guix-data-service/web/render.scm
index 081399a..744c66c 100644
--- a/guix-data-service/web/render.scm
+++ b/guix-data-service/web/render.scm
@@ -24,6 +24,7 @@
   #:use-module (srfi srfi-19)
   #:use-module (srfi srfi-26)
   #:use-module (ice-9 ftw)
+  #:use-module (ice-9 iconv)
   #:use-module (ice-9 binary-ports)
   #:use-module (web request)
   #:use-module (web response)
@@ -142,30 +143,39 @@
   (list (build-response
          #:code code
          #:headers (append extra-headers
-                           '((content-type . (text/html))
+                           '((content-type . (text/html
+                                              (charset . "utf-8")))
                              (vary . (accept)))))
-        (lambda (port)
-          (sxml->html sxml port))))
+        (call-with-encoded-output-string
+         "utf-8"
+         (lambda (port)
+           (sxml->html sxml port)))))
 
 (define* (render-json json #:key (extra-headers '())
                       (code 200))
   (list (build-response
          #:code code
          #:headers (append extra-headers
-                           '((content-type . (application/json))
+                           '((content-type . (application/json
+                                              (charset . "utf-8")))
                              (vary . (accept)))))
-        (lambda (port)
-          (scm->json json port))))
+        (call-with-encoded-output-string
+         "utf-8"
+         (lambda (port)
+           (scm->json json port)))))
 
 (define* (render-text text #:key (extra-headers '())
                       (code 200))
   (list (build-response
          #:code code
          #:headers (append extra-headers
-                           '((content-type . (text/plain))
+                           '((content-type . (text/plain
+                                              (charset . "utf-8")))
                              (vary . (accept)))))
-        (lambda (port)
-          (display text port))))
+        (call-with-encoded-output-string
+         "utf-8"
+         (lambda (port)
+           (display text port)))))
 
 (define (not-found uri)
   (list (build-response #:code 404)