diff --git a/nongnu/system/linux-initrd.scm b/nongnu/system/linux-initrd.scm
index cb83845..460d48d 100644
--- a/nongnu/system/linux-initrd.scm
+++ b/nongnu/system/linux-initrd.scm
@@ -19,6 +19,7 @@
   #:use-module (guix modules)
   #:use-module (guix utils)
   #:use-module (nongnu packages linux)
+  #:use-module (nonguix modules)
   #:export (microcode-initrd))
 
 ;; See https://www.kernel.org/doc/Documentation/x86/microcode.txt
@@ -45,7 +46,7 @@ MICROCODE-PACKAGES, in the format expected by the kernel."
                             '((gnu build linux-initrd)
                               (guix build utils)
                               (nonguix build utils))
-                            #:select? (const #t))
+                            #:select? nonguix-module-name?)
       #~(begin
           (use-modules (gnu build linux-initrd)
                        (guix build utils)
@@ -83,7 +84,7 @@ MICROCODE-PACKAGES, in the format expected by the kernel."
     (with-imported-modules (source-module-closure
                             '((guix build utils)
                               (nonguix build utils))
-                            #:select? (const #t))
+                            #:select? nonguix-module-name?)
       #~(begin
           (use-modules (guix build utils)
                        (nonguix build utils))
diff --git a/nonguix/modules.scm b/nonguix/modules.scm
new file mode 100644
index 0000000..570a8bb
--- /dev/null
+++ b/nonguix/modules.scm
@@ -0,0 +1,27 @@
+;;; Copyright © 2020 Alex Griffin <a@ajgrf.com>
+;;;
+;;; This program is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; This program is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+(define-module (nonguix modules)
+  #:use-module (ice-9 match)
+  #:export (nonguix-module-name?))
+
+(define (nonguix-module-name? name)
+  "Return true if NAME (a list of symbols) denotes a Guix or Nonguix module."
+  (match name
+    (('guix _ ...) #t)
+    (('gnu _ ...) #t)
+    (('nonguix _ ...) #t)
+    (('nongnu _ ...) #t)
+    (_ #f)))