diff --git a/lib/system/orc.nim b/lib/system/orc.nim
index 1935407102..b7b98c3404 100644
--- a/lib/system/orc.nim
+++ b/lib/system/orc.nim
@@ -411,7 +411,7 @@ proc registerCycle(s: Cell; desc: PNimTypeV2) =
   if roots.d == nil: init(roots)
   add(roots, s, desc)
 
-  if roots.len >= rootsThreshold+defaultThreshold:
+  if roots.len - defaultThreshold >= rootsThreshold:
     collectCycles()
   when logOrc:
     writeCell("[added root]", s, desc)
diff --git a/tests/gc/tdisable_orc.nim b/tests/gc/tdisable_orc.nim
new file mode 100644
index 0000000000..b5f161c791
--- /dev/null
+++ b/tests/gc/tdisable_orc.nim
@@ -0,0 +1,9 @@
+discard """
+  joinable: false
+"""
+
+import std/asyncdispatch
+
+# bug #22256
+GC_disableMarkAndSweep()
+waitFor sleepAsync(1000)