diff --git a/include/jemalloc/internal/cache_bin.h b/include/jemalloc/internal/cache_bin.h
index a56b4a1d..c016769d 100644
--- a/include/jemalloc/internal/cache_bin.h
+++ b/include/jemalloc/internal/cache_bin.h
@@ -20,6 +20,16 @@
  */
 typedef uint16_t cache_bin_sz_t;
 
+/*
+ * That implies the following value, for the maximum number of items in any
+ * individual bin.  The cache bins track their bounds looking just at the low
+ * bits of a pointer, compared against a cache_bin_sz_t.  So that's
+ *   1 << (sizeof(cache_bin_sz_t) * 8)
+ * bytes spread across pointer sized objects to get the maximum.
+ */
+#define CACHE_BIN_NCACHED_MAX (((size_t)1 << sizeof(cache_bin_sz_t) * 8) \
+    / sizeof(void *) - 1)
+
 /*
  * This lives inside the cache_bin (for locality reasons), and is initialized
  * alongside it, but is otherwise not modified by any cache bin operations.
diff --git a/src/cache_bin.c b/src/cache_bin.c
index 51b87499..1e26c4ef 100644
--- a/src/cache_bin.c
+++ b/src/cache_bin.c
@@ -6,6 +6,7 @@
 void
 cache_bin_info_init(cache_bin_info_t *info,
     cache_bin_sz_t ncached_max) {
+	assert(ncached_max <= CACHE_BIN_NCACHED_MAX);
 	size_t stack_size = (size_t)ncached_max * sizeof(void *);
 	assert(stack_size < ((size_t)1 << (sizeof(cache_bin_sz_t) * 8)));
 	info->ncached_max = (cache_bin_sz_t)ncached_max;