diff --git a/qemu/saimaa.c b/qemu/saimaa.c
index 35c220b..eefea03 100644
--- a/qemu/saimaa.c
+++ b/qemu/saimaa.c
@@ -25,7 +25,9 @@
 #define SAIMAA_UEFI_BASE     0x10000000
 #define SAIMAA_UEFI_SIZE     0x04000000
 #define SAIMAA_RPM_BASE      0x00400000
-#define SAIMAA_RPM_SIZE      0x07C00000 /* 0x00400000..0x08000000 heap-ish */
+/* Ends before peripheral window 0x07800000 (SDC/USB/UART live there;
+ * a bigger region shadows MMIO with silent RAM!). */
+#define SAIMAA_RPM_SIZE      0x07400000 /* 0x00400000..0x07800000 */
 #define SAIMAA_OCIMEM_BASE   0x00200000
 #define SAIMAA_OCIMEM_SIZE   0x00100000
 #define SAIMAA_DDRLOW_BASE   0x08000000