diff -r 8f3d62c9905e -r d426a6a7cf05 configs/example/fs.py
--- a/configs/example/fs.py	Thu Oct 25 18:38:03 2012 +0100
+++ b/configs/example/fs.py	Thu Oct 25 18:38:21 2012 +0100
@@ -128,8 +128,11 @@
     test_sys.iobridge.master = test_sys.membus.slave
 
 # Sanity check
-if options.fastmem and (options.caches or options.l2cache):
-    fatal("You cannot use fastmem in combination with caches!")
+if options.fastmem:
+    if TestCPUClass != AtomicSimpleCPU:
+        fatal("Fastmem can only be used with atomic CPU!")
+    if (options.caches or options.l2cache):
+        fatal("You cannot use fastmem in combination with caches!")
 
 for i in xrange(np):
     if options.fastmem: