diff --git a/lib/System/Unix/Program.inc b/lib/System/Unix/Program.inc
index 4da1c73..896e809 100644
--- a/lib/System/Unix/Program.inc
+++ b/lib/System/Unix/Program.inc
@@ -119,7 +119,7 @@
   getrlimit (RLIMIT_DATA, &r);
   r.rlim_cur = limit;
   setrlimit (RLIMIT_DATA, &r);
-#ifndef __CYGWIN__
+#ifdef RLIMIT_RSS
   // Resident set size.
   getrlimit (RLIMIT_RSS, &r);
   r.rlim_cur = limit;