diff --git a/include/jemalloc/internal/rtree.h b/include/jemalloc/internal/rtree.h
index fc88dfec..9c6cc22f 100644
--- a/include/jemalloc/internal/rtree.h
+++ b/include/jemalloc/internal/rtree.h
@@ -23,9 +23,6 @@ typedef struct rtree_s rtree_t;
 #define	RTREE_HEIGHT_MAX						\
     ((1U << (LG_SIZEOF_PTR+3)) / RTREE_BITS_PER_LEVEL)
 
-/* Used for two-stage lock-free node initialization. */
-#define	RTREE_NODE_INITIALIZING	((rtree_elm_t *)0x1)
-
 #define	RTREE_CTX_INITIALIZER	{					\
 	false,								\
 	0,								\
@@ -139,6 +136,7 @@ struct rtree_s {
 	 */
 	unsigned		start_level[RTREE_HEIGHT_MAX + 1];
 	rtree_level_t		levels[RTREE_HEIGHT_MAX];
+	malloc_mutex_t		init_lock;
 };
 
 #endif /* JEMALLOC_H_STRUCTS */
@@ -251,7 +249,7 @@ JEMALLOC_ALWAYS_INLINE bool
 rtree_node_valid(rtree_elm_t *node)
 {
 
-	return ((uintptr_t)node > (uintptr_t)RTREE_NODE_INITIALIZING);
+	return ((uintptr_t)node != (uintptr_t)0);
 }
 
 JEMALLOC_ALWAYS_INLINE rtree_elm_t *
diff --git a/include/jemalloc/internal/witness.h b/include/jemalloc/internal/witness.h
index 26024ac2..86ddb64a 100644
--- a/include/jemalloc/internal/witness.h
+++ b/include/jemalloc/internal/witness.h
@@ -28,7 +28,8 @@ typedef int witness_comp_t (const witness_t *, void *, const witness_t *,
 #define	WITNESS_RANK_ARENA_EXTENT_CACHE	10
 
 #define	WITNESS_RANK_RTREE_ELM		11U
-#define	WITNESS_RANK_BASE		12U
+#define	WITNESS_RANK_RTREE		12U
+#define	WITNESS_RANK_BASE		13U
 
 #define	WITNESS_RANK_LEAF		0xffffffffU
 #define	WITNESS_RANK_ARENA_BIN		WITNESS_RANK_LEAF
diff --git a/src/rtree.c b/src/rtree.c
index 0a42a982..b6b9ed76 100644
--- a/src/rtree.c
+++ b/src/rtree.c
@@ -59,6 +59,8 @@ rtree_new(rtree_t *rtree, unsigned bits)
 	}
 	rtree->start_level[RTREE_HEIGHT_MAX] = 0;
 
+	malloc_mutex_init(&rtree->init_lock, "rtree", WITNESS_RANK_RTREE);
+
 	return (false);
 }
 
@@ -135,25 +137,18 @@ rtree_node_init(tsdn_t *tsdn, rtree_t *rtree, unsigned level,
 {
 	rtree_elm_t *node;
 
-	if (atomic_cas_p((void **)elmp, NULL, RTREE_NODE_INITIALIZING)) {
-		spin_t spinner;
-
-		/*
-		 * Another thread is already in the process of initializing.
-		 * Spin-wait until initialization is complete.
-		 */
-		spin_init(&spinner);
-		do {
-			spin_adaptive(&spinner);
-			node = atomic_read_p((void **)elmp);
-		} while (node == RTREE_NODE_INITIALIZING);
-	} else {
+	malloc_mutex_lock(tsdn, &rtree->init_lock);
+	node = atomic_read_p((void**)elmp);
+	if (node == NULL) {
 		node = rtree_node_alloc(tsdn, rtree, ZU(1) <<
 		    rtree->levels[level].bits);
-		if (node == NULL)
+		if (node == NULL) {
+			malloc_mutex_unlock(tsdn, &rtree->init_lock);
 			return (NULL);
+		}
 		atomic_write_p((void **)elmp, node);
 	}
+	malloc_mutex_unlock(tsdn, &rtree->init_lock);
 
 	return (node);
 }
diff --git a/test/unit/rtree.c b/test/unit/rtree.c
index a05834fa..03f4e269 100644
--- a/test/unit/rtree.c
+++ b/test/unit/rtree.c
@@ -13,8 +13,10 @@ rtree_node_alloc_intercept(tsdn_t *tsdn, rtree_t *rtree, size_t nelms)
 	if (rtree != test_rtree)
 		return rtree_node_alloc_orig(tsdn, rtree, nelms);
 
+	malloc_mutex_unlock(tsdn, &rtree->init_lock);
 	node = (rtree_elm_t *)calloc(nelms, sizeof(rtree_elm_t));
 	assert_ptr_not_null(node, "Unexpected calloc() failure");
+	malloc_mutex_lock(tsdn, &rtree->init_lock);
 
 	return (node);
 }