diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -331,6 +331,8 @@
 static bool cache_alloc(uma_zone_t, uma_cache_t, void *, int);
 static bool cache_free(uma_zone_t, uma_cache_t, void *, int);
 
+static void check_align_mask(unsigned mask);
+
 static int sysctl_vm_zone_count(SYSCTL_HANDLER_ARGS);
 static int sysctl_vm_zone_stats(SYSCTL_HANDLER_ARGS);
 static int sysctl_handle_uma_zone_allocs(SYSCTL_HANDLER_ARGS);
@@ -3249,13 +3251,26 @@
 	return (zone_alloc_item(kegs, &args, UMA_ANYDOMAIN, M_WAITOK));
 }
 
+
+static void
+check_align_mask(unsigned mask)
+{
+
+	if (__predict_false(!powerof2(mask + 1)))
+		panic("UMA: %s: Not the mask of a power of 2 (%#x)",
+		    __func__, mask);
+	if (__predict_false(mask & (1U << 31)))
+		panic("UMA: %s: Mask too big (%#x)", __func__, mask);
+}
+
 /* Public functions */
 /* See uma.h */
 void
 uma_set_cache_align_mask(unsigned mask)
 {
 
-	uma_cache_align_mask = mask & ~(1U << 31);
+	check_align_mask(mask);
+	uma_cache_align_mask = mask;
 }
 
 unsigned
@@ -3273,8 +3288,7 @@
 	struct uma_zctor_args args;
 	uma_zone_t res;
 
-	KASSERT(powerof2(align + 1), ("invalid zone alignment %d for \"%s\"",
-	    align, name));
+	check_align_mask(align);
 
 	/* This stuff is essential for the zone ctor */
 	memset(&args, 0, sizeof(args));