diff --git a/doc/guix.texi b/doc/guix.texi
index aeeec617e..a16422261 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -5582,7 +5582,7 @@ $ guix challenge @var{package}
 
 @noindent
 where @var{package} is a package specification such as
-@code{guile-2.0} or @code{glibc:debug}.
+@code{guile@@2.0} or @code{glibc:debug}.
 
 The general syntax is:
 
@@ -5590,6 +5590,11 @@ The general syntax is:
 guix challenge @var{options} [@var{packages}@dots{}]
 @end example
 
+When a difference is found between the hash of a locally-built item and
+that of a server-provided substitute, or among substitutes provided by
+different servers, the command displays it as in the example above and
+exits with a non-zero return code.
+
 The one option that matters is:
 
 @table @code
diff --git a/guix/scripts/challenge.scm b/guix/scripts/challenge.scm
index 4a0c865b0..0eb49da0c 100644
--- a/guix/scripts/challenge.scm
+++ b/guix/scripts/challenge.scm
@@ -233,9 +233,11 @@ Challenge the substitutes for PACKAGE... provided by one or more servers.\n"))
 
            (run-with-store store
              (mlet* %store-monad ((items  (mapm %store-monad
-                                               ensure-store-item files))
+                                                ensure-store-item files))
                                   (issues (discrepancies items urls)))
                (for-each summarize-discrepancy issues)
+               (unless (null? issues)
+                 (exit 1))
                (return (null? issues)))
              #:system system)))))))
 
diff --git a/scripts/guix.in b/scripts/guix.in
index 8f2d8a643..5d6921dd0 100644
--- a/scripts/guix.in
+++ b/scripts/guix.in
@@ -64,4 +64,9 @@
       (apply guix-main (command-line))))
 
   (maybe-augment-load-paths!)
+
+  ;; XXX: It would be more convenient to change it to:
+  ;;   (exit (run-guix-main))
+  ;; but since the 'guix' command is not updated by 'guix pull', we cannot
+  ;; really do it now.
   (run-guix-main))