diff --git a/libguile/finalizers.c b/libguile/finalizers.c
index 47495b595..f6e67d5d7 100644
--- a/libguile/finalizers.c
+++ b/libguile/finalizers.c
@@ -327,7 +327,15 @@ spawn_finalizer_thread (void)
   start_finalization_thread ();
 }
 
-#endif /* SCM_USE_PTHREAD_THREADS */
+#else /* !SCM_USE_PTHREAD_THREADS */
+
+int
+scm_i_is_finalizer_thread (struct scm_thread *t)
+{
+  return 0;
+}
+
+#endif /* !SCM_USE_PTHREAD_THREADS */