diff --git a/gnu/packages.scm b/gnu/packages.scm
index 5d60423a3a..f55c294a18 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -313,7 +313,7 @@ use NAME@VERSION instead~%")))
         new)
        (#f
         pkg)))
-    (_
+    (x
      (if version
          (leave (_ "~A: package not found for version ~a~%") name version)
          (if (not fallback?)
diff --git a/guix/scripts/build.scm b/guix/scripts/build.scm
index 86b95b4075..a9f649d2ee 100644
--- a/guix/scripts/build.scm
+++ b/guix/scripts/build.scm
@@ -195,7 +195,7 @@ of \"guile\"."
              ((old new)
               (cons (specification->package old)
                     (specification->package new)))
-             (_
+             (x
               (leave (_ "invalid replacement specification: ~s~%") spec))))
          replacement-specs))
 
diff --git a/guix/scripts/hash.scm b/guix/scripts/hash.scm
index a57602ab51..a6eced92fb 100644
--- a/guix/scripts/hash.scm
+++ b/guix/scripts/hash.scm
@@ -149,5 +149,5 @@ and 'hexadecimal' can be used as well).\n"))
          (lambda args
            (leave (_ "~a~%")
                   (strerror (system-error-errno args))))))
-      (_
+      (x
        (leave (_ "wrong number of arguments~%"))))))
diff --git a/guix/scripts/import/gnu.scm b/guix/scripts/import/gnu.scm
index 92bd8305ea..66861f5837 100644
--- a/guix/scripts/import/gnu.scm
+++ b/guix/scripts/import/gnu.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2016 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -68,7 +68,7 @@ Return a package declaration template for PACKAGE, a GNU package.\n"))
                      ((or "interactive" "always" "never")
                       (alist-cons 'key-download (string->symbol arg)
                                   result))
-                     (_
+                     (x
                       (leave (_ "unsupported policy: ~a~%")
                              arg)))))
          %standard-import-options))
@@ -99,7 +99,7 @@ Return a package declaration template for PACKAGE, a GNU package.\n"))
        (with-error-handling
          (gnu->guix-package name
                             #:key-download (assoc-ref opts 'key-download))))
-      (_
+      (x
        (leave (_ "wrong number of arguments~%"))))))
 
 ;;; gnu.scm ends here
diff --git a/guix/scripts/import/nix.scm b/guix/scripts/import/nix.scm
index dba053b313..05e6e4b85d 100644
--- a/guix/scripts/import/nix.scm
+++ b/guix/scripts/import/nix.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2016 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2014 David Thompson <davet@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -86,5 +86,5 @@ Import and convert the Nix expression ATTRIBUTE of NIXPKGS.\n"))
          (format #t ";; converted from ~a:~a~%~%"
                  (location-file loc) (location-line loc))
          expr))
-      (_
+      (x
        (leave (_ "wrong number of arguments~%"))))))
diff --git a/guix/scripts/offload.scm b/guix/scripts/offload.scm
index 7db0c9d610..b278f1e313 100644
--- a/guix/scripts/offload.scm
+++ b/guix/scripts/offload.scm
@@ -118,7 +118,7 @@ determined."
          (primitive-load file))))
     (lambda args
       (match args
-        (('system-error . _)
+        (('system-error . rest)
          (let ((err (system-error-errno args)))
            ;; Silently ignore missing file since this is a common case.
            (if (= ENOENT err)
@@ -129,7 +129,7 @@ determined."
          (let ((loc (source-properties->location properties)))
            (leave (_ "~a: ~a~%")
                   (location->string loc) message)))
-        (_
+        (x
          (leave (_ "failed to load machine file '~a': ~s~%")
                 file args))))))
 
diff --git a/guix/scripts/refresh.scm b/guix/scripts/refresh.scm
index b00ac98c96..84e2a8f2a6 100644
--- a/guix/scripts/refresh.scm
+++ b/guix/scripts/refresh.scm
@@ -105,7 +105,7 @@
                     ((or "interactive" "always" "never")
                      (alist-cons 'key-download (string->symbol arg)
                                  result))
-                    (_
+                    (x
                      (leave (_ "unsupported policy: ~a~%")
                             arg)))))
 
diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index 8827c45fb8..21e0613a8a 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -300,7 +300,7 @@ Otherwise return #f."
 (define (narinfo-signature->canonical-sexp str)
   "Return the value of a narinfo's 'Signature' field as a canonical sexp."
   (match (string-split str #\;)
-    ((version _ sig)
+    ((version host-name sig)
      (let ((maybe-number (string->number version)))
        (cond ((not (number? maybe-number))
               (leave (_ "signature version must be a number: ~s~%")
diff --git a/guix/ui.scm b/guix/ui.scm
index 452d16308e..eb85df3b18 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -247,7 +247,7 @@ messages."
   "Report the failure to load FILE, a user-provided Scheme file.
 ARGS is the list of arguments received by the 'throw' handler."
   (match args
-    (('system-error . _)
+    (('system-error . rest)
      (let ((err (system-error-errno args)))
        (report-error (_ "failed to load '~a': ~a~%") file (strerror err))))
     (('syntax-error proc message properties form . rest)
@@ -264,7 +264,7 @@ ARGS is the list of arguments received by the 'throw' handler."
   "Report the failure to load FILE, a user-provided Scheme file, without
 exiting.  ARGS is the list of arguments received by the 'throw' handler."
   (match args
-    (('system-error . _)
+    (('system-error . rest)
      (let ((err (system-error-errno args)))
        (warning (_ "failed to load '~a': ~a~%") file (strerror err))))
     (('syntax-error proc message properties form . rest)
@@ -409,7 +409,7 @@ interpreted."
           ("ZB"  (expt 10 21))
           ("YB"  (expt 10 24))
           (""    1)
-          (_
+          (x
            (leave (_ "unknown unit: ~a~%") unit)))))))
 
 (define (call-with-error-handling thunk)
@@ -535,7 +535,7 @@ similar."
 error."
   (match (read/eval str)
     ((? package? p) p)
-    (_
+    (x
      (leave (_ "expression ~s does not evaluate to a package~%")
             str))))