diff --git a/tests/test_cpp.cc b/tests/test_cpp.cc
index 802b7008f9..9d3f64acb3 100644
--- a/tests/test_cpp.cc
+++ b/tests/test_cpp.cc
@@ -952,6 +952,31 @@ void TestArena() {
   }
 }
 
+void TestInlinedArena() {
+  int n = 100000;
+
+  struct Decrementer {
+    Decrementer(int* _p) : p(_p) {}
+    ~Decrementer() { (*p)--; }
+    int* p;
+  };
+
+  {
+    upb::InlinedArena<1024> arena;
+    for (int i = 0; i < n; i++) {
+      arena.Own(new Decrementer(&n));
+
+      // Intersperse allocation and ensure we can write to it.
+      int* val = static_cast<int*>(upb_arena_malloc(arena.ptr(), sizeof(int)));
+      *val = i;
+    }
+
+    // Test a large allocation.
+    upb_arena_malloc(arena.ptr(), 1000000);
+  }
+  ASSERT(n == 0);
+}
+
 extern "C" {
 
 int run_tests() {
diff --git a/upb/upb.hpp b/upb/upb.hpp
index a3ec5faff8..b7b99761fb 100644
--- a/upb/upb.hpp
+++ b/upb/upb.hpp
@@ -41,6 +41,9 @@ class Arena {
  public:
   // A simple arena with no initial memory block and the default allocator.
   Arena() : ptr_(upb_arena_new(), upb_arena_free) {}
+  Arena(char *initial_block, size_t size)
+      : ptr_(upb_arena_init(initial_block, size, &upb_alloc_global),
+             upb_arena_free) {}
 
   upb_arena* ptr() { return ptr_.get(); }
 
@@ -71,15 +74,12 @@ class Arena {
 template <int N>
 class InlinedArena : public Arena {
  public:
-  InlinedArena() : ptr_(upb_arena_new(&initial_block_, N, &upb_alloc_global)) {}
-
-  upb_arena* ptr() { return ptr_.get(); }
+  InlinedArena() : Arena(initial_block_, N) {}
 
  private:
   InlinedArena(const InlinedArena*) = delete;
   InlinedArena& operator=(const InlinedArena*) = delete;
 
-  std::unique_ptr<upb_arena, decltype(&upb_arena_free)> ptr_;
   char initial_block_[N];
 };