diff --git a/arch/sandbox/cpu/cpu.c b/arch/sandbox/cpu/cpu.c
index 636d354..248d17a 100644
--- a/arch/sandbox/cpu/cpu.c
+++ b/arch/sandbox/cpu/cpu.c
@@ -230,7 +230,7 @@
 	return mentry->tag;
 }
 
-unsigned int sandbox_read(const void *addr, enum sandboxio_size_t size)
+unsigned long sandbox_read(const void *addr, enum sandboxio_size_t size)
 {
 	struct sandbox_state *state = state_get_current();