diff --git a/include/jemalloc/internal/pages.h b/include/jemalloc/internal/pages.h
index 3d7993dd..ad1f606a 100644
--- a/include/jemalloc/internal/pages.h
+++ b/include/jemalloc/internal/pages.h
@@ -13,6 +13,9 @@
 /* Return the smallest pagesize multiple that is >= s. */
 #define PAGE_CEILING(s)							\
 	(((s) + PAGE_MASK) & ~PAGE_MASK)
+/* Return the largest pagesize multiple that is <=s. */
+#define PAGE_FLOOR(s) 							\
+	((s) & ~PAGE_MASK)
 
 /* Huge page size.  LG_HUGEPAGE is determined by the configure script. */
 #define HUGEPAGE	((size_t)(1U << LG_HUGEPAGE))
diff --git a/src/sec.c b/src/sec.c
index 6fffaf1e..c13904d8 100644
--- a/src/sec.c
+++ b/src/sec.c
@@ -25,7 +25,7 @@ sec_init(tsdn_t *tsdn, sec_t *sec, base_t *base, pai_t *fallback,
     const sec_opts_t *opts) {
 	assert(opts->max_alloc > 0);
 
-	size_t max_alloc = opts->max_alloc & ~PAGE_MASK;
+	size_t max_alloc = PAGE_FLOOR(opts->max_alloc);
 	pszind_t npsizes = sz_psz2ind(max_alloc) + 1;
 
 	size_t sz_shards = opts->nshards * sizeof(sec_shard_t);