diff --git a/guix/build/download-nar.scm b/guix/build/download-nar.scm
index 377e428341..867f3c10bb 100644
--- a/guix/build/download-nar.scm
+++ b/guix/build/download-nar.scm
@@ -20,7 +20,7 @@
   #:use-module (guix build download)
   #:use-module (guix build utils)
   #:use-module ((guix serialization) #:hide (dump-port*))
-  #:use-module (guix zlib)
+  #:autoload   (zlib) (call-with-gzip-input-port)
   #:use-module (guix progress)
   #:use-module (web uri)
   #:use-module (srfi srfi-11)
diff --git a/guix/cvs-download.scm b/guix/cvs-download.scm
index cb42103aae..76b3eac739 100644
--- a/guix/cvs-download.scm
+++ b/guix/cvs-download.scm
@@ -60,35 +60,26 @@
   "Return a fixed-output derivation that fetches REF, a <cvs-reference>
 object.  The output is expected to have recursive hash HASH of type
 HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
-  (define zlib
-    (module-ref (resolve-interface '(gnu packages compression)) 'zlib))
-
-  (define config.scm
-    (scheme-file "config.scm"
-                 #~(begin
-                     (define-module (guix config)
-                       #:export (%libz))
-
-                     (define %libz
-                       #+(file-append zlib "/lib/libz")))))
+  (define guile-zlib
+    (module-ref (resolve-interface '(gnu packages guile)) 'guile-zlib))
 
   (define modules
-    (cons `((guix config) => ,config.scm)
-          (delete '(guix config)
-                  (source-module-closure '((guix build cvs)
-                                           (guix build download-nar))))))
+    (delete '(guix config)
+            (source-module-closure '((guix build cvs)
+                                     (guix build download-nar)))))
   (define build
     (with-imported-modules modules
-      #~(begin
-          (use-modules (guix build cvs)
-                       (guix build download-nar))
+      (with-extensions (list guile-zlib)
+        #~(begin
+            (use-modules (guix build cvs)
+                         (guix build download-nar))
 
-          (or (cvs-fetch '#$(cvs-reference-root-directory ref)
-                         '#$(cvs-reference-module ref)
-                         '#$(cvs-reference-revision ref)
-                         #$output
-                         #:cvs-command (string-append #+cvs "/bin/cvs"))
-              (download-nar #$output)))))
+            (or (cvs-fetch '#$(cvs-reference-root-directory ref)
+                           '#$(cvs-reference-module ref)
+                           '#$(cvs-reference-revision ref)
+                           #$output
+                           #:cvs-command (string-append #+cvs "/bin/cvs"))
+                (download-nar #$output))))))
 
   (mlet %store-monad ((guile (package->derivation guile system)))
     (gexp->derivation (or name "cvs-checkout") build
diff --git a/guix/git-download.scm b/guix/git-download.scm
index 71ea1031c5..90634a8c4c 100644
--- a/guix/git-download.scm
+++ b/guix/git-download.scm
@@ -84,35 +84,26 @@ HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
           ("tar" ,(module-ref (resolve-interface '(gnu packages base))
                               'tar)))))
 
-  (define zlib
-    (module-ref (resolve-interface '(gnu packages compression)) 'zlib))
-
   (define guile-json
     (module-ref (resolve-interface '(gnu packages guile)) 'guile-json-3))
 
+  (define guile-zlib
+    (module-ref (resolve-interface '(gnu packages guile)) 'guile-zlib))
+
   (define gnutls
     (module-ref (resolve-interface '(gnu packages tls)) 'gnutls))
 
-  (define config.scm
-    (scheme-file "config.scm"
-                 #~(begin
-                     (define-module (guix config)
-                       #:export (%libz))
-
-                     (define %libz
-                       #+(file-append zlib "/lib/libz")))))
-
   (define modules
-    (cons `((guix config) => ,config.scm)
-          (delete '(guix config)
-                  (source-module-closure '((guix build git)
-                                           (guix build utils)
-                                           (guix build download-nar)
-                                           (guix swh))))))
+    (delete '(guix config)
+            (source-module-closure '((guix build git)
+                                     (guix build utils)
+                                     (guix build download-nar)
+                                     (guix swh)))))
 
   (define build
     (with-imported-modules modules
-      (with-extensions (list guile-json gnutls)   ;for (guix swh)
+      (with-extensions (list guile-json gnutls   ;for (guix swh)
+                             guile-zlib)
         #~(begin
             (use-modules (guix build git)
                          (guix build utils)
diff --git a/guix/hg-download.scm b/guix/hg-download.scm
index 4cdc1a780a..694105ceba 100644
--- a/guix/hg-download.scm
+++ b/guix/hg-download.scm
@@ -60,35 +60,26 @@
   "Return a fixed-output derivation that fetches REF, a <hg-reference>
 object.  The output is expected to have recursive hash HASH of type
 HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
-  (define zlib
-    (module-ref (resolve-interface '(gnu packages compression)) 'zlib))
-
-  (define config.scm
-    (scheme-file "config.scm"
-                 #~(begin
-                     (define-module (guix config)
-                       #:export (%libz))
-
-                     (define %libz
-                       #+(file-append zlib "/lib/libz")))))
+  (define guile-zlib
+    (module-ref (resolve-interface '(gnu packages guile)) 'guile-zlib))
 
   (define modules
-    (cons `((guix config) => ,config.scm)
-          (delete '(guix config)
-                  (source-module-closure '((guix build hg)
-                                           (guix build download-nar))))))
+    (delete '(guix config)
+            (source-module-closure '((guix build hg)
+                                     (guix build download-nar)))))
 
   (define build
     (with-imported-modules modules
-      #~(begin
-          (use-modules (guix build hg)
-                       (guix build download-nar))
+      (with-extensions (list guile-zlib)
+        #~(begin
+            (use-modules (guix build hg)
+                         (guix build download-nar))
 
-          (or (hg-fetch '#$(hg-reference-url ref)
-                        '#$(hg-reference-changeset ref)
-                        #$output
-                        #:hg-command (string-append #+hg "/bin/hg"))
-              (download-nar #$output)))))
+            (or (hg-fetch '#$(hg-reference-url ref)
+                          '#$(hg-reference-changeset ref)
+                          #$output
+                          #:hg-command (string-append #+hg "/bin/hg"))
+                (download-nar #$output))))))
 
   (mlet %store-monad ((guile (package->derivation guile system)))
     (gexp->derivation (or name "hg-checkout") build