diff --git a/memory.c b/memory.c
index 9938b6ba45..34a088e90f 100644
--- a/memory.c
+++ b/memory.c
@@ -840,7 +840,7 @@ static uint64_t unassigned_mem_read(void *opaque, hwaddr addr,
     if (current_cpu != NULL) {
         cpu_unassigned_access(current_cpu, addr, false, false, 0, size);
     }
-    return 0;
+    return -1ULL;
 }
 
 static void unassigned_mem_write(void *opaque, hwaddr addr,