diff --git a/io.c b/io.c
index eb12d95fe4..a1158a2b86 100644
--- a/io.c
+++ b/io.c
@@ -6202,7 +6202,7 @@ fptr_copy_finalizer(rb_io_t *fptr, const rb_io_t *orig)
 #if defined(__CYGWIN__) || !defined(HAVE_WORKING_FORK)
     void (*const old_finalize)(struct rb_io_t*,int) = fptr->finalize;
 
-    if (old_finalize == fptr->finalize) return;
+    if (old_finalize == orig->finalize) return;
 #endif
 
     fptr->finalize = orig->finalize;