diff --git a/src/rez/package_cache.py b/src/rez/package_cache.py
index 0f8335756..e4e5eac85 100644
--- a/src/rez/package_cache.py
+++ b/src/rez/package_cache.py
@@ -506,7 +506,7 @@ def add_variants(self, variants: Iterable[Variant], package_cache_async: bool =
         # a prod install. On non-windows we could fork instead, but there would
         # remain no good solution on windows.
         #
-        if not system.is_production_rez_install:
+        if package_cache_async and not system.is_production_rez_install:
             raise PackageCacheError(
                 "PackageCache.add_variants is only supported in a "
                 "production rez installation."