diff --git a/include/jemalloc/internal/extent_externs.h b/include/jemalloc/internal/extent_externs.h
index 5d53aad1..8aba5763 100644
--- a/include/jemalloc/internal/extent_externs.h
+++ b/include/jemalloc/internal/extent_externs.h
@@ -24,7 +24,7 @@ size_t extent_size_quantize_floor(size_t size);
 size_t extent_size_quantize_ceil(size_t size);
 #endif
 
-rb_proto(, extent_avail_, extent_tree_t, extent_t)
+ph_proto(, extent_avail_, extent_tree_t, extent_t)
 ph_proto(, extent_heap_, extent_heap_t, extent_t)
 
 bool extents_init(tsdn_t *tsdn, extents_t *extents, extent_state_t state,