diff --git a/Fleece/Support/RefCounted.cc b/Fleece/Support/RefCounted.cc
index 93ee9ce0..72185e98 100644
--- a/Fleece/Support/RefCounted.cc
+++ b/Fleece/Support/RefCounted.cc
@@ -136,7 +136,7 @@ namespace fleece {
     namespace internal {
         /// Tag bit that's added to `_ref` while accessing it.
         /// We can't use the low bit (1) because mutable Fleece Values already use that as a tag.
-        static constexpr uintptr_t kBusyMask = uintptr_t(1) << 63;
+        static constexpr uintptr_t kBusyMask = uintptr_t(1) << (8 * sizeof(uintptr_t) - 1);
 
         AtomicWrapper::AtomicWrapper(uintptr_t ref) noexcept
         :_ref(ref)
diff --git a/Tests/SupportTests.cc b/Tests/SupportTests.cc
index 2acff0bb..a27f368b 100644
--- a/Tests/SupportTests.cc
+++ b/Tests/SupportTests.cc
@@ -473,7 +473,7 @@ struct AtomicRetainedTest : RefCounted {
 
 TEST_CASE("AtomicRetained") {
     // This is mostly to check for compile errors.
-    AtomicRef r = new AtomicRetainedTest();
+    AtomicRef<AtomicRetainedTest> r = new AtomicRetainedTest();
     CHECK(r->i == 0);
     AtomicRetained r2 = r;
     AtomicRetained r3 = std::move(r2);