diff --git a/src/refcount.c b/src/refcount.c
index bac38f6..db604d6 100644
--- a/src/refcount.c
+++ b/src/refcount.c
@@ -765,11 +765,17 @@ bool refcount_context_add_destructor(const RefcountContext *ctx, void *obj,
     }
     entry->callback = callback;
     entry->user_data = user_data;
-    if (!ht_insert(ENTRY->destructors, key, entry)) {
+    if (!lock_entry_mtx(ENTRY)) {
         refcount_free(&ctx->alloc, entry);
         return false;
     }
-    return true;
+    bool success = true;
+    if (!ht_insert(ENTRY->destructors, key, entry)) {
+        refcount_free(&ctx->alloc, entry);
+        success = false;
+    }
+    unlock_entry_mtx(ENTRY);
+    return success;
 }
 
 /**
@@ -782,5 +788,10 @@ bool refcount_context_add_destructor(const RefcountContext *ctx, void *obj,
  */
 bool refcount_context_remove_destructor(const RefcountContext *ctx, void *obj,
                                         void *key) {
-    return ht_remove(ENTRY->destructors, key);
+    if (!lock_entry_mtx(ENTRY)) {
+        return false;
+    }
+    bool success = ht_remove(ENTRY->destructors, key);
+    unlock_entry_mtx(ENTRY);
+    return success;
 }