diff --git a/sys/kern/kern_malloc.c b/sys/kern/kern_malloc.c
--- a/sys/kern/kern_malloc.c
+++ b/sys/kern/kern_malloc.c
@@ -768,20 +768,31 @@
     struct malloc_type *mtp, struct domainset *ds, int flags)
 {
 	void *res;
+	size_t asize;
 
 	KASSERT(align != 0 && powerof2(align),
 	    ("malloc_domainset_aligned: wrong align %#zx size %#zx",
 	    align, size));
-	KASSERT(align <= kmemzones[nitems(kmemzones) - 2].kz_size,
+	KASSERT(align <= PAGE_SIZE,
 	    ("malloc_domainset_aligned: align %#zx (size %#zx) too large",
 	    align, size));
 
-	if (size < align)
-		size = align;
-	res = malloc_domainset(size, mtp, ds, flags);
+	/*
+	 * Round the allocation size up to the next power of 2,
+	 * because we can only guarantee alignment for
+	 * power-of-2-sized allocations.  Further increase the
+	 * allocation size to align if the rounded size is less than
+	 * the align, since malloc zones provide alignment equal to
+	 * size.
+	 */
+	asize = size == 0 ? align : 1UL << flsl(size - 1);
+	if (asize < align)
+		asize = align;
+
+	res = malloc_domainset(asize, mtp, ds, flags);
 	KASSERT(res == NULL || ((uintptr_t)res & (align - 1)) == 0,
 	    ("malloc_domainset_aligned: result not aligned %p size %#zx "
-	    "align %#zx", res, size, align));
+	    "allocsize %#zx align %#zx", res, size, asize, align));
 	return (res);
 }
 
@@ -1173,7 +1184,7 @@
 
 		align = UMA_ALIGN_PTR;
 		if (powerof2(size) && size > sizeof(void *))
-			align = size - 1;
+			align = MIN(size, PAGE_SIZE) - 1;
 		for (subzone = 0; subzone < numzones; subzone++) {
 			kmemzones[indx].kz_zone[subzone] =
 			    uma_zcreate(name, size,