diff --git a/jemalloc/src/jemalloc.c b/jemalloc/src/jemalloc.c
index f252f591..a79752eb 100644
--- a/jemalloc/src/jemalloc.c
+++ b/jemalloc/src/jemalloc.c
@@ -101,8 +101,8 @@ arenas_extend(unsigned ind)
 	arena_t *ret;
 
 	/* Allocate enough space for trailing bins. */
-	ret = (arena_t *)base_alloc(sizeof(arena_t)
-	    + (sizeof(arena_bin_t) * (nbins - 1)));
+	ret = (arena_t *)base_alloc(offsetof(arena_t, bins)
+	    + (sizeof(arena_bin_t) * nbins));
 	if (ret != NULL && arena_new(ret, ind) == false) {
 		arenas[ind] = ret;
 		return (ret);
diff --git a/jemalloc/src/rtree.c b/jemalloc/src/rtree.c
index a583751d..7753743c 100644
--- a/jemalloc/src/rtree.c
+++ b/jemalloc/src/rtree.c
@@ -13,11 +13,12 @@ rtree_new(unsigned bits)
 		height++;
 	assert(height * bits_per_level >= bits);
 
-	ret = (rtree_t*)base_alloc(sizeof(rtree_t) + (sizeof(unsigned) *
-	    (height - 1)));
+	ret = (rtree_t*)base_alloc(offsetof(rtree_t, level2bits) +
+	    (sizeof(unsigned) * height));
 	if (ret == NULL)
 		return (NULL);
-	memset(ret, 0, sizeof(rtree_t) + (sizeof(unsigned) * (height - 1)));
+	memset(ret, 0, offsetof(rtree_t, level2bits) + (sizeof(unsigned) *
+	    height));
 
 	malloc_mutex_init(&ret->mutex);
 	ret->height = height;
diff --git a/jemalloc/src/tcache.c b/jemalloc/src/tcache.c
index ef69b1ae..3fb8f2bd 100644
--- a/jemalloc/src/tcache.c
+++ b/jemalloc/src/tcache.c
@@ -204,7 +204,7 @@ tcache_create(arena_t *arena)
 	size_t size;
 	unsigned i;
 
-	size = sizeof(tcache_t) + (sizeof(tcache_bin_t) * (nhbins - 1));
+	size = offsetof(tcache_t, tbins) + (sizeof(tcache_bin_t) * nhbins);
 	/*
 	 * Round up to the nearest multiple of the cacheline size, in order to
 	 * avoid the possibility of false cacheline sharing.