diff --git a/include/configs/MPC8548CDS.h b/include/configs/MPC8548CDS.h
index 687fe84..14936c2 100644
--- a/include/configs/MPC8548CDS.h
+++ b/include/configs/MPC8548CDS.h
@@ -340,7 +340,7 @@
 
 /*
  * General PCI
- * Addresses are mapped 1-1.
+ * Memory space is mapped 1-1, but I/O space must start from 0.
  */
 #define CFG_PCI1_MEM_BASE	0x80000000
 #define CFG_PCI1_MEM_PHYS	CFG_PCI1_MEM_BASE