diff --git a/include/jemalloc/internal/jemalloc_internal_inlines_a.h b/include/jemalloc/internal/jemalloc_internal_inlines_a.h
index 5ec35db3..c6a1f7eb 100644
--- a/include/jemalloc/internal/jemalloc_internal_inlines_a.h
+++ b/include/jemalloc/internal/jemalloc_internal_inlines_a.h
@@ -151,6 +151,7 @@ pre_reentrancy(tsd_t *tsd, arena_t *arena) {
 	assert(arena != arena_get(tsd_tsdn(tsd), 0, false));
 
 	bool fast = tsd_fast(tsd);
+	assert(tsd_reentrancy_level_get(tsd) < INT8_MAX);
 	++*tsd_reentrancy_levelp_get(tsd);
 	if (fast) {
 		/* Prepare slow path for reentrancy. */
diff --git a/src/extent.c b/src/extent.c
index f464de4a..3f1c76fd 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -1028,7 +1028,18 @@ extent_alloc_default(extent_hooks_t *extent_hooks, void *new_addr, size_t size,
 static void
 extent_hook_pre_reentrancy(tsdn_t *tsdn, arena_t *arena) {
 	tsd_t *tsd = tsdn_null(tsdn) ? tsd_fetch() : tsdn_tsd(tsdn);
-	pre_reentrancy(tsd, arena);
+	if (arena == arena_get(tsd_tsdn(tsd), 0, false)) {
+		/*
+		 * The only legitimate case of customized extent hooks for a0 is
+		 * hooks with no allocation activities.  One such example is to
+		 * place metadata on pre-allocated resources such as huge pages.
+		 * In that case, rely on reentrancy_level checks to catch
+		 * infinite recursions.
+		 */
+		pre_reentrancy(tsd, NULL);
+	} else {
+		pre_reentrancy(tsd, arena);
+	}
 }
 
 static void