diff --git a/src/segment.c b/src/segment.c
index 4bb4aaf5..b3fc60ee 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -518,6 +518,12 @@ static void mi_segment_os_free(mi_segment_t* segment, size_t segment_size, mi_se
 // called from `heap_collect`. 
 void _mi_segments_collect(bool force, mi_segments_tld_t* tld) {
   mi_pages_try_purge(force,tld);
+  #if MI_DEBUG>=2
+  if (!_mi_is_main_thread()) {
+    mi_assert_internal(tld->pages_purge.first == NULL);
+    mi_assert_internal(tld->pages_purge.last == NULL);
+  }
+  #endif
 }