1 files changed, 13 insertions, 2 deletions
diff --git a/guix/gexp.scm b/guix/gexp.scm
index f7c064297b..5b5b064b59 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -920,7 +920,18 @@ and in the current monad setting (system type, etc.)"
               (simple-format #f "~a:~a" line column)))
         "<unknown location>")))
 
-(define-syntax-parameter current-imported-modules
+(define-syntax-rule (define-syntax-parameter-once name proc)
+  ;; Like 'define-syntax-parameter' but ensure the top-level binding for NAME
+  ;; does not get redefined.  This works around a race condition in a
+  ;; multi-threaded context with Guile <= 2.2.4: <https://bugs.gnu.org/27476>.
+  (eval-when (load eval expand compile)
+    (define name
+      (if (module-locally-bound? (current-module) 'name)
+          (module-ref (current-module) 'name)
+          (make-syntax-transformer 'name 'syntax-parameter
+                                   (list proc))))))
+
+(define-syntax-parameter-once current-imported-modules
   ;; Current list of imported modules.
   (identifier-syntax '()))
 
@@ -931,7 +942,7 @@ environment."
                          (identifier-syntax modules)))
     body ...))
 
-(define-syntax-parameter current-imported-extensions
+(define-syntax-parameter-once current-imported-extensions
   ;; Current list of extensions.
   (identifier-syntax '()))