diff --git a/sys/amd64/include/vmparam.h b/sys/amd64/include/vmparam.h
--- a/sys/amd64/include/vmparam.h
+++ b/sys/amd64/include/vmparam.h
@@ -239,16 +239,19 @@
  * because the result is not actually accessed until later, but the early
  * vt fb startup needs to be reworked.
  */
+#define	PHYS_IN_DMAP(pa)	(dmaplimit == 0 || (pa) < dmaplimit)
+#define	VIRT_IN_DMAP(va)	((va) >= DMAP_MIN_ADDRESS &&		\
+    (va) < (DMAP_MIN_ADDRESS + dmaplimit))
+
 #define	PMAP_HAS_DMAP	1
 #define	PHYS_TO_DMAP(x)	({						\
-	KASSERT(dmaplimit == 0 || (x) < dmaplimit,			\
+	KASSERT(PHYS_IN_DMAP(x),					\
 	    ("physical address %#jx not covered by the DMAP",		\
 	    (uintmax_t)x));						\
 	(x) | DMAP_MIN_ADDRESS; })
 
 #define	DMAP_TO_PHYS(x)	({						\
-	KASSERT((x) < (DMAP_MIN_ADDRESS + dmaplimit) &&			\
-	    (x) >= DMAP_MIN_ADDRESS,					\
+	KASSERT(VIRT_IN_DMAP(x),					\
 	    ("virtual address %#jx not covered by the DMAP",		\
 	    (uintmax_t)x));						\
 	(x) & ~DMAP_MIN_ADDRESS; })