Index: libcxx/include/latch
===================================================================
--- libcxx/include/latch
+++ libcxx/include/latch
@@ -75,7 +75,11 @@
     }
 
     inline _LIBCPP_INLINE_VISIBILITY
-    constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected) { }
+    constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected)
+    {
+        _LIBCPP_ASSERT_UNCATEGORIZED(__expected >= 0,
+                                     "__expected cannot be negative");
+    }
 
     _LIBCPP_HIDE_FROM_ABI ~latch() = default;
     latch(const latch&) = delete;
@@ -84,6 +88,8 @@
     inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
     void count_down(ptrdiff_t __update = 1)
     {
+        _LIBCPP_ASSERT_UNCATEGORIZED(
+            __update >= 0, "latch::count_down called with a negative value");
         auto const __old = __a_.fetch_sub(__update, memory_order_release);
         if(__old == __update)
             __a_.notify_all();
@@ -103,6 +109,8 @@
     inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
     void arrive_and_wait(ptrdiff_t __update = 1)
     {
+        _LIBCPP_ASSERT_UNCATEGORIZED(
+            __update >= 0, "latch::arrive_and_wait called with a negative value");
         count_down(__update);
         wait();
     }