diff --git a/include/nlohmann/detail/view/builder.hpp b/include/nlohmann/detail/view/builder.hpp
index 11187a947..eb3d70792 100644
--- a/include/nlohmann/detail/view/builder.hpp
+++ b/include/nlohmann/detail/view/builder.hpp
@@ -415,8 +415,10 @@ class builder
             arena_ensure(16);
             std::memcpy(m_arena_write, r, 16);
         }
-        else
+        else if (n != 0)
         {
+            // (an empty run leaves an empty arena unallocated, and memcpy()
+            // must not be passed its null pointer even for zero bytes)
             arena_ensure(n);
             std::memcpy(m_arena_write, r, n);
         }
diff --git a/single_include/nlohmann/json_view.hpp b/single_include/nlohmann/json_view.hpp
index 26e30cbbb..0de60773b 100644
--- a/single_include/nlohmann/json_view.hpp
+++ b/single_include/nlohmann/json_view.hpp
@@ -1039,8 +1039,10 @@ class builder
             arena_ensure(16);
             std::memcpy(m_arena_write, r, 16);
         }
-        else
+        else if (n != 0)
         {
+            // (an empty run leaves an empty arena unallocated, and memcpy()
+            // must not be passed its null pointer even for zero bytes)
             arena_ensure(n);
             std::memcpy(m_arena_write, r, n);
         }