Index: sys/dev/iommu/iommu_gas.c
===================================================================
--- sys/dev/iommu/iommu_gas.c
+++ sys/dev/iommu/iommu_gas.c
@@ -384,7 +384,7 @@
 		iommu_gas_match_insert(a);
 		return (0);
 	}
-	if (entry->free_down < a->size + a->offset + IOMMU_PAGE_SIZE)
+	if (entry->free_down < a->size + a->offset + 2 * IOMMU_PAGE_SIZE)
 		return (ENOMEM);
 	if (entry->first >= a->common->lowaddr)
 		return (ENOMEM);
@@ -408,7 +408,7 @@
 {
 	struct iommu_map_entry *child;
 
-	if (entry->free_down < a->size + a->offset + IOMMU_PAGE_SIZE)
+	if (entry->free_down < a->size + a->offset + 2 * IOMMU_PAGE_SIZE)
 		return (ENOMEM);
 	if (entry->last < a->common->highaddr)
 		return (ENOMEM);