diff --git a/build-aux/hydra/demo-os.scm b/build-aux/hydra/demo-os.scm
index 9164500d70..d96cdce496 100644
--- a/build-aux/hydra/demo-os.scm
+++ b/build-aux/hydra/demo-os.scm
@@ -37,7 +37,7 @@
 (operating-system
  (host-name "gnu")
  (timezone "Europe/Paris")
- (locale "en_US.UTF-8")
+ (locale "en_US.utf8")
 
  (bootloader (grub-configuration
               (device "/dev/sda")))
diff --git a/gnu/system/install.scm b/gnu/system/install.scm
index d3d6764a70..01e79480b1 100644
--- a/gnu/system/install.scm
+++ b/gnu/system/install.scm
@@ -221,7 +221,7 @@ Use Alt-F2 for documentation.
   (operating-system
     (host-name "gnu")
     (timezone "Europe/Paris")
-    (locale "en_US.UTF-8")
+    (locale "en_US.utf8")
     (bootloader (grub-configuration
                  (device "/dev/sda")))
     (file-systems