diff --git a/exec.c b/exec.c
index f923043763c6982492910959508d17406556f232..08914aecdea88361b17cfc6c0f635e84695e8e00 100644
--- a/exec.c
+++ b/exec.c
@@ -80,7 +80,7 @@ typedef struct PageDesc {
 
 typedef struct PhysPageDesc {
     /* offset in host memory of the page + io_index in the low 12 bits */
-    unsigned long phys_offset;
+    uint32_t phys_offset;
 } PhysPageDesc;
 
 typedef struct VirtPageDesc {