diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index d19b4d8..10188fe 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -173,8 +173,8 @@
 status_t Parcel::finishFlattenBinder(const sp<IBinder>& binder)
 {
     internal::Stability::tryMarkCompilationUnit(binder.get());
-    auto category = internal::Stability::getCategory(binder.get());
-    return writeInt32(category.repr());
+    int16_t rep = internal::Stability::getCategory(binder.get()).repr();
+    return writeInt32(rep);
 }
 
 status_t Parcel::finishUnflattenBinder(
@@ -184,7 +184,8 @@
     status_t status = readInt32(&stability);
     if (status != OK) return status;
 
-    status = internal::Stability::setRepr(binder.get(), stability, true /*log*/);
+    status = internal::Stability::setRepr(binder.get(), static_cast<int16_t>(stability),
+                                          true /*log*/);
     if (status != OK) return status;
 
     *out = binder;
diff --git a/libs/binder/Stability.cpp b/libs/binder/Stability.cpp
index 601ce96..dac3819 100644
--- a/libs/binder/Stability.cpp
+++ b/libs/binder/Stability.cpp
@@ -33,7 +33,6 @@
 Stability::Category Stability::Category::currentFromLevel(Level level) {
     return {
         .version = kBinderWireFormatVersion,
-        .reserved = {0},
         .level = level,
     };
 }
diff --git a/libs/binder/include/binder/Binder.h b/libs/binder/include/binder/Binder.h
index 754f87c..27db32c 100644
--- a/libs/binder/include/binder/Binder.h
+++ b/libs/binder/include/binder/Binder.h
@@ -119,10 +119,12 @@
     std::atomic<Extras*> mExtras;
 
     friend ::android::internal::Stability;
-    union {
-        int32_t mStability;
-        void* mReserved0;
-    };
+    int16_t mStability;
+    int16_t mReserved0;
+
+#ifdef __LP64__
+    int32_t mReserved1;
+#endif
 };
 
 // ---------------------------------------------------------------------------
diff --git a/libs/binder/include/binder/Stability.h b/libs/binder/include/binder/Stability.h
index 6bc607f..629b565 100644
--- a/libs/binder/include/binder/Stability.h
+++ b/libs/binder/include/binder/Stability.h
@@ -136,14 +136,15 @@
         VINTF = 0b111111,
     };
 
-    // This is the format of stability passed on the wire.
+    // This is the format of stability passed on the wire. It is only 2 bytes
+    // long, but 2 bytes in addition to this are reserved here. The difference
+    // in size is in order to free up space in BBinder, which is fixed by
+    // prebuilts inheriting from it.
     struct Category {
-        static inline Category fromRepr(int32_t representation) {
+        static inline Category fromRepr(int16_t representation) {
             return *reinterpret_cast<Category*>(&representation);
         }
-        int32_t repr() const {
-            return *reinterpret_cast<const int32_t*>(this);
-        }
+        int16_t repr() const { return *reinterpret_cast<const int16_t*>(this); }
         static inline Category currentFromLevel(Level level);
 
         bool operator== (const Category& o) const {
@@ -161,12 +162,10 @@
         // class must write parcels according to the version documented here.
         uint8_t version;
 
-        uint8_t reserved[2];
-
         // bitmask of Stability::Level
         Level level;
     };
-    static_assert(sizeof(Category) == sizeof(int32_t));
+    static_assert(sizeof(Category) == sizeof(int16_t));
 
     // returns the stability according to how this was built
     static Level getLocalLevel();