diff --git a/gnu/packages.scm b/gnu/packages.scm
index 1af3b8d440..42f3546606 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -148,15 +148,16 @@ (define %package-module-path
   (let* ((not-colon   (char-set-complement (char-set #\:)))
          (environment (string-tokenize (or (getenv "GUIX_PACKAGE_PATH") "")
                                        not-colon))
-         (channels-scm channels-go (package-path-entries)))
+         (channels-scm (package-path-entries)))
     ;; Automatically add channels and items from $GUIX_PACKAGE_PATH to Guile's
     ;; search path.  For historical reasons, $GUIX_PACKAGE_PATH goes to the
     ;; front; channels go to the back so that they don't override Guix' own
     ;; modules.
+    (add-channels-to-load-path!)
     (set! %load-path
-      (append environment %load-path channels-scm))
+      (append environment %load-path))
     (set! %load-compiled-path
-      (append environment %load-compiled-path channels-go))
+      (append environment %load-compiled-path))

     (make-parameter
      (append environment
diff --git a/guix/describe.scm b/guix/describe.scm
index a4ca2462f4..6694b1eaf7 100644
--- a/guix/describe.scm
+++ b/guix/describe.scm
@@ -27,6 +27,7 @@ (define-module (guix describe)
                                 sexp->channel
                                 manifest-entry-channel)
   #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-34)
   #:use-module (ice-9 match)
   #:export (current-profile
@@ -34,6 +35,7 @@ (define-module (guix describe)
             current-profile-entries
             current-channels
             package-path-entries
+            add-channels-to-load-path!

             package-provenance
             package-channels
@@ -190,6 +192,21 @@ (define (package-path-entries)
                                       "/site-ccache")))
                (current-channel-entries))))

+(define add-channels-to-load-path!
+  (let ((promise
+         (delay
+           (let-values (((channels-scm channels-go) (package-path-entries)))
+             (set! %load-path
+                   (append %load-path channels-scm))
+             (set! %load-compiled-path
+                   (append %load-compiled-path channels-go))))))
+    (lambda ()
+      "Automatically add channels to Guile's search path.  Channels are added
+to the end of the path so they don't override Guix' own modules.  This
+function ensures that channels are only added to the search path once even if
+it is called multiple times."
+      (force promise))))
+
 (define (package-channels package)
   "Return the list of channels providing PACKAGE or an empty list if it could
 not be determined."
diff --git a/guix/self.scm b/guix/self.scm
index 2652688c71..28239d53f5 100644
--- a/guix/self.scm
+++ b/guix/self.scm
@@ -882,6 +882,7 @@ (define* (compiled-guix source #:key
                     ,(local-file "../guix/store/schema.sql")))

                  #:extensions (list guile-gcrypt
+                                    guile-git     ;for (guix git)
                                     guile-json)   ;for (guix swh)
                  #:guile-for-build guile-for-build))

diff --git a/guix/ui.scm b/guix/ui.scm
index eba12c8616..87ae24ea55 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -38,6 +38,7 @@
 (define-module (guix ui)                       ;import in user interfaces only
   #:use-module (guix i18n)
   #:use-module (guix colors)
+  #:use-module (guix describe)
   #:use-module (guix diagnostics)
   #:use-module (guix gexp)
   #:use-module (guix sets)
@@ -2192,9 +2193,14 @@ (define* (command-files #:optional directory)

 (define (extension-directories)
   "Return the list of directories containing Guix extensions."
-  (filter file-exists?
-          (parse-path
-           (getenv "GUIX_EXTENSIONS_PATH"))))
+  (add-channels-to-load-path!)
+  (let ((channels (package-path-entries)))
+    (filter file-exists?
+            (parse-path
+             (getenv "GUIX_EXTENSIONS_PATH")
+             (map
+              (cut string-append <> "/guix/extensions")
+              channels)))))

 (define (commands)
   "Return the list of commands, alphabetically sorted."
