diff --git a/guix/build-system/perl.scm b/guix/build-system/perl.scm
index 7c6deb34bf..0d5493ab90 100644
--- a/guix/build-system/perl.scm
+++ b/guix/build-system/perl.scm
@@ -133,7 +133,9 @@ provides a `Makefile.PL' file as its build system."
                                                     search-paths))
                             #:make-maker? #$make-maker?
                             #:make-maker-flags #$make-maker-flags
-                            #:module-build-flags #$(sexp->gexp module-build-flags)
+                            #:module-build-flags #$(if (pair? module-build-flags)
+                                                       (sexp->gexp module-build-flags)
+                                                       module-build-flags)
                             #:phases #$(if (pair? phases)
                                            (sexp->gexp phases)
                                            phases)