diff --git a/upb/mem/BUILD b/upb/mem/BUILD
index 71e007e544..f6bc19e7f1 100644
--- a/upb/mem/BUILD
+++ b/upb/mem/BUILD
@@ -46,10 +46,12 @@ cc_test(
     deps = [
         "@com_google_googletest//:gtest_main",
         "//upb:mem",
+        "//upb:mem_internal",
         "//upb:port",
         "@com_google_absl//absl/random",
         "@com_google_absl//absl/random:distributions",
         "@com_google_absl//absl/synchronization",
+        "@com_google_absl//absl/time",
     ],
 )
 
diff --git a/upb/mem/arena.c b/upb/mem/arena.c
index 7e34f86ee4..b9d3d9d8f9 100644
--- a/upb/mem/arena.c
+++ b/upb/mem/arena.c
@@ -346,3 +346,23 @@ bool upb_Arena_Fuse(upb_Arena* a1, upb_Arena* a2) {
     }
   }
 }
+
+void upb_Arena_IncRefFor(upb_Arena* arena, const void* owner) {
+  _upb_ArenaRoot r;
+retry:
+  r = _upb_Arena_FindRoot(arena);
+  if (upb_Atomic_CompareExchangeWeak(
+          &r.root->parent_or_count, &r.tagged_count,
+          _upb_Arena_TaggedFromRefcount(
+              _upb_Arena_RefCountFromTagged(r.tagged_count) + 1),
+          memory_order_release, memory_order_acquire)) {
+    // We incremented it successfully, so we are done.
+    return;
+  }
+  // We failed update due to parent switching on the arena.
+  goto retry;
+}
+
+void upb_Arena_DecRefFor(upb_Arena* arena, const void* owner) {
+  upb_Arena_Free(arena);
+}
diff --git a/upb/mem/arena.h b/upb/mem/arena.h
index e7fd852ff9..e4afceaa43 100644
--- a/upb/mem/arena.h
+++ b/upb/mem/arena.h
@@ -47,6 +47,9 @@ UPB_API upb_Arena* upb_Arena_Init(void* mem, size_t n, upb_alloc* alloc);
 UPB_API void upb_Arena_Free(upb_Arena* a);
 UPB_API bool upb_Arena_Fuse(upb_Arena* a, upb_Arena* b);
 
+void upb_Arena_IncRefFor(upb_Arena* arena, const void* owner);
+void upb_Arena_DecRefFor(upb_Arena* arena, const void* owner);
+
 void* _upb_Arena_SlowMalloc(upb_Arena* a, size_t size);
 size_t upb_Arena_SpaceAllocated(upb_Arena* arena);
 uint32_t upb_Arena_DebugRefCount(upb_Arena* arena);
diff --git a/upb/mem/arena_test.cc b/upb/mem/arena_test.cc
index 7020da1344..0b13e1a365 100644
--- a/upb/mem/arena_test.cc
+++ b/upb/mem/arena_test.cc
@@ -19,6 +19,8 @@
 #include "absl/synchronization/notification.h"
 
 // Must be last.
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
 #include "upb/port/def.inc"
 
 namespace {
@@ -44,7 +46,7 @@ TEST(ArenaTest, FuseWithInitialBlock) {
   char buf2[1024];
   upb_Arena* arenas[] = {upb_Arena_Init(buf1, 1024, &upb_alloc_global),
                          upb_Arena_Init(buf2, 1024, &upb_alloc_global),
-                         upb_Arena_Init(NULL, 0, &upb_alloc_global)};
+                         upb_Arena_Init(nullptr, 0, &upb_alloc_global)};
   int size = sizeof(arenas) / sizeof(arenas[0]);
   for (int i = 0; i < size; ++i) {
     for (int j = 0; j < size; ++j) {
@@ -74,6 +76,15 @@ class Environment {
     if (old != nullptr) upb_Arena_Free(old);
   }
 
+  void RandomIncRefCount(absl::BitGen& gen) {
+    auto* a = SwapRandomly(gen, nullptr);
+    if (a != nullptr) {
+      upb_Arena_IncRefFor(a, nullptr);
+      upb_Arena_DecRefFor(a, nullptr);
+      upb_Arena_Free(a);
+    }
+  }
+
   void RandomFuse(absl::BitGen& gen) {
     std::array<upb_Arena*, 2> old;
     for (auto& o : old) {
@@ -168,6 +179,40 @@ TEST(ArenaTest, FuzzFuseFuseRace) {
   for (auto& t : threads) t.join();
 }
 
+TEST(ArenaTest, ArenaIncRef) {
+  upb_Arena* arena1 = upb_Arena_New();
+  EXPECT_EQ(upb_Arena_DebugRefCount(arena1), 1);
+  upb_Arena_IncRefFor(arena1, nullptr);
+  EXPECT_EQ(upb_Arena_DebugRefCount(arena1), 2);
+  upb_Arena_DecRefFor(arena1, nullptr);
+  EXPECT_EQ(upb_Arena_DebugRefCount(arena1), 1);
+  upb_Arena_Free(arena1);
+}
+
+TEST(ArenaTest, FuzzFuseIncRefCountRace) {
+  Environment env;
+
+  absl::Notification done;
+  std::vector<std::thread> threads;
+  for (int i = 0; i < 10; ++i) {
+    threads.emplace_back([&]() {
+      absl::BitGen gen;
+      while (!done.HasBeenNotified()) {
+        env.RandomNewFree(gen);
+      }
+    });
+  }
+
+  absl::BitGen gen;
+  auto end = absl::Now() + absl::Seconds(2);
+  while (absl::Now() < end) {
+    env.RandomFuse(gen);
+    env.RandomIncRefCount(gen);
+  }
+  done.Notify();
+  for (auto& t : threads) t.join();
+}
+
 #endif
 
 }  // namespace