diff --git a/sys/platform/pc64/x86_64/nexus.c b/sys/platform/pc64/x86_64/nexus.c
--- a/sys/platform/pc64/x86_64/nexus.c
+++ b/sys/platform/pc64/x86_64/nexus.c
@@ -459,7 +459,7 @@
 	 */
 	if ((rman_get_bustag(r) == X86_64_BUS_SPACE_MEM) &&
 	    (rman_get_end(r) >= 1024 * 1024)) {
-		u_int32_t psize;
+		u_int64_t psize;
 
 		psize = rman_get_size(r);
 		pmap_unmapdev((vm_offset_t)rman_get_virtual(r), psize);