diff --git a/dawn.json b/dawn.json
index dac7ff1..edb9057 100644
--- a/dawn.json
+++ b/dawn.json
@@ -240,7 +240,9 @@
             {"value": 0, "name": "success"},
             {"value": 1, "name": "error"},
             {"value": 2, "name": "unknown"},
-            {"value": 3, "name": "device lost"}
+            {"value": 3, "name": "device lost"},
+            {"value": 4, "name": "destroyed before callback"},
+            {"value": 5, "name": "unmapped before callback"}
         ]
     },
     "buffer usage": {
diff --git a/src/dawn_native/Buffer.cpp b/src/dawn_native/Buffer.cpp
index 1a2fbc2..aa9af0a 100644
--- a/src/dawn_native/Buffer.cpp
+++ b/src/dawn_native/Buffer.cpp
@@ -138,7 +138,7 @@
     BufferBase::~BufferBase() {
         if (mState == BufferState::Mapped) {
             ASSERT(!IsError());
-            CallMapCallback(mMapSerial, WGPUBufferMapAsyncStatus_Unknown);
+            CallMapCallback(mMapSerial, WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
         }
     }
 
@@ -302,13 +302,13 @@
         ASSERT(!IsError());
 
         if (mState == BufferState::Mapped) {
-            Unmap();
+            UnmapInternal(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
         } else if (mState == BufferState::MappedAtCreation) {
             if (mStagingBuffer != nullptr) {
                 mStagingBuffer.reset();
             } else if (mSize != 0) {
                 ASSERT(IsCPUWritableAtCreation());
-                Unmap();
+                UnmapInternal(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
             }
         }
 
@@ -330,6 +330,10 @@
     }
 
     void BufferBase::Unmap() {
+        UnmapInternal(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback);
+    }
+
+    void BufferBase::UnmapInternal(WGPUBufferMapAsyncStatus callbackStatus) {
         if (IsError()) {
             // It is an error to call Unmap() on an ErrorBuffer, but we still need to reclaim the
             // fake mapped staging data.
@@ -346,7 +350,7 @@
             // completed before the Unmap.
             // Callbacks are not fired if there is no callback registered, so this is correct for
             // mappedAtCreation = true.
-            CallMapCallback(mMapSerial, WGPUBufferMapAsyncStatus_Unknown);
+            CallMapCallback(mMapSerial, callbackStatus);
             UnmapImpl();
 
             mMapCallback = nullptr;
diff --git a/src/dawn_native/Buffer.h b/src/dawn_native/Buffer.h
index 39ba68c..fc6353c 100644
--- a/src/dawn_native/Buffer.h
+++ b/src/dawn_native/Buffer.h
@@ -79,8 +79,6 @@
 
         void DestroyInternal();
 
-        bool IsMapped() const;
-
         MaybeError MapAtCreationInternal();
 
       private:
@@ -104,6 +102,7 @@
         MaybeError ValidateUnmap() const;
         MaybeError ValidateDestroy() const;
         bool CanGetMappedRange(bool writable, size_t offset, size_t size) const;
+        void UnmapInternal(WGPUBufferMapAsyncStatus callbackStatus);
 
         uint64_t mSize = 0;
         wgpu::BufferUsage mUsage = wgpu::BufferUsage::None;
diff --git a/src/dawn_wire/client/Buffer.cpp b/src/dawn_wire/client/Buffer.cpp
index aad0253..7db4749 100644
--- a/src/dawn_wire/client/Buffer.cpp
+++ b/src/dawn_wire/client/Buffer.cpp
@@ -102,8 +102,8 @@
 
     Buffer::~Buffer() {
         // Callbacks need to be fired in all cases, as they can handle freeing resources
-        // so we call them with "Unknown" status.
-        ClearMapRequests(WGPUBufferMapAsyncStatus_Unknown);
+        // so we call them with "DestroyedBeforeCallback" status.
+        ClearMapRequests(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
     }
 
     void Buffer::ClearMapRequests(WGPUBufferMapAsyncStatus status) {
@@ -326,7 +326,7 @@
         mMappedData = nullptr;
         mMapOffset = 0;
         mMapSize = 0;
-        ClearMapRequests(WGPUBufferMapAsyncStatus_Unknown);
+        ClearMapRequests(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback);
 
         BufferUnmapCmd cmd;
         cmd.self = ToAPI(this);
@@ -338,7 +338,7 @@
         mWriteHandle = nullptr;
         mReadHandle = nullptr;
         mMappedData = nullptr;
-        ClearMapRequests(WGPUBufferMapAsyncStatus_Unknown);
+        ClearMapRequests(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
 
         BufferDestroyCmd cmd;
         cmd.self = ToAPI(this);
diff --git a/src/tests/unittests/validation/BufferValidationTests.cpp b/src/tests/unittests/validation/BufferValidationTests.cpp
index 325b760..1c93b07 100644
--- a/src/tests/unittests/validation/BufferValidationTests.cpp
+++ b/src/tests/unittests/validation/BufferValidationTests.cpp
@@ -317,7 +317,8 @@
         wgpu::Buffer buf = CreateMapReadBuffer(4);
         buf.MapAsync(wgpu::MapMode::Read, 0, 4, ToMockBufferMapAsyncCallback, nullptr);
 
-        EXPECT_CALL(*mockBufferMapAsyncCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _))
+        EXPECT_CALL(*mockBufferMapAsyncCallback,
+                    Call(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback, _))
             .Times(1);
         buf.Unmap();
 
@@ -328,7 +329,8 @@
         wgpu::Buffer buf = CreateMapWriteBuffer(4);
         buf.MapAsync(wgpu::MapMode::Write, 0, 4, ToMockBufferMapAsyncCallback, nullptr);
 
-        EXPECT_CALL(*mockBufferMapAsyncCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _))
+        EXPECT_CALL(*mockBufferMapAsyncCallback,
+                    Call(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback, _))
             .Times(1);
         buf.Unmap();
 
@@ -344,7 +346,8 @@
         wgpu::Buffer buf = CreateMapReadBuffer(4);
         buf.MapAsync(wgpu::MapMode::Read, 0, 4, ToMockBufferMapAsyncCallback, this + 0);
 
-        EXPECT_CALL(*mockBufferMapAsyncCallback, Call(WGPUBufferMapAsyncStatus_Unknown, this + 0))
+        EXPECT_CALL(*mockBufferMapAsyncCallback,
+                    Call(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback, this + 0))
             .Times(1);
         buf.Unmap();
 
@@ -357,7 +360,8 @@
         wgpu::Buffer buf = CreateMapWriteBuffer(4);
         buf.MapAsync(wgpu::MapMode::Write, 0, 4, ToMockBufferMapAsyncCallback, this + 0);
 
-        EXPECT_CALL(*mockBufferMapAsyncCallback, Call(WGPUBufferMapAsyncStatus_Unknown, this + 0))
+        EXPECT_CALL(*mockBufferMapAsyncCallback,
+                    Call(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback, this + 0))
             .Times(1);
         buf.Unmap();
 
@@ -374,7 +378,8 @@
         wgpu::Buffer buf = CreateMapReadBuffer(4);
         buf.MapAsync(wgpu::MapMode::Read, 0, 4, ToMockBufferMapAsyncCallback, nullptr);
 
-        EXPECT_CALL(*mockBufferMapAsyncCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _))
+        EXPECT_CALL(*mockBufferMapAsyncCallback,
+                    Call(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback, _))
             .Times(1);
         buf.Destroy();
 
@@ -385,7 +390,8 @@
         wgpu::Buffer buf = CreateMapWriteBuffer(4);
         buf.MapAsync(wgpu::MapMode::Write, 0, 4, ToMockBufferMapAsyncCallback, nullptr);
 
-        EXPECT_CALL(*mockBufferMapAsyncCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _))
+        EXPECT_CALL(*mockBufferMapAsyncCallback,
+                    Call(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback, _))
             .Times(1);
         buf.Destroy();
 
diff --git a/src/tests/unittests/wire/WireBufferMappingTests.cpp b/src/tests/unittests/wire/WireBufferMappingTests.cpp
index ccef844..c763ac0 100644
--- a/src/tests/unittests/wire/WireBufferMappingTests.cpp
+++ b/src/tests/unittests/wire/WireBufferMappingTests.cpp
@@ -137,8 +137,10 @@
     EXPECT_CALL(api, BufferGetConstMappedRange(apiBuffer, 0, kBufferSize))
         .WillOnce(Return(&bufferContent));
 
-    // Destroy before the client gets the success, so the callback is called with unknown.
-    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _)).Times(1);
+    // Destroy before the client gets the success, so the callback is called with
+    // DestroyedBeforeCallback.
+    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback, _))
+        .Times(1);
     wgpuBufferRelease(buffer);
     EXPECT_CALL(api, BufferRelease(apiBuffer));
 
@@ -146,8 +148,8 @@
     FlushServer();
 }
 
-// Check the map read callback is called with UNKNOWN when the map request would have worked, but
-// Unmap was called
+// Check the map read callback is called with "UnmappedBeforeCallback" when the map request would
+// have worked, but Unmap was called
 TEST_F(WireBufferMappingTests, UnmapCalledTooEarlyForRead) {
     wgpuBufferMapAsync(buffer, WGPUMapMode_Read, 0, kBufferSize, ToMockBufferMapCallback, nullptr);
 
@@ -161,7 +163,8 @@
     FlushClient();
 
     // Oh no! We are calling Unmap too early!
-    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _)).Times(1);
+    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback, _))
+        .Times(1);
     wgpuBufferUnmap(buffer);
 
     // The callback shouldn't get called, even when the request succeeded on the server side
@@ -304,8 +307,8 @@
     EXPECT_EQ(nullptr, wgpuBufferGetMappedRange(buffer, 0, kBufferSize));
 }
 
-// Check that the map write callback is called with UNKNOWN when the buffer is destroyed before the
-// request is finished
+// Check that the map write callback is called with "DestroyedBeforeCallback" when the buffer is
+// destroyed before the request is finished
 TEST_F(WireBufferMappingTests, DestroyBeforeWriteRequestEnd) {
     wgpuBufferMapAsync(buffer, WGPUMapMode_Write, 0, kBufferSize, ToMockBufferMapCallback, nullptr);
 
@@ -317,8 +320,10 @@
     EXPECT_CALL(api, BufferGetMappedRange(apiBuffer, 0, kBufferSize))
         .WillOnce(Return(&bufferContent));
 
-    // Destroy before the client gets the success, so the callback is called with unknown.
-    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _)).Times(1);
+    // Destroy before the client gets the success, so the callback is called with
+    // DestroyedBeforeCallback.
+    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback, _))
+        .Times(1);
     wgpuBufferRelease(buffer);
     EXPECT_CALL(api, BufferRelease(apiBuffer));
 
@@ -326,8 +331,8 @@
     FlushServer();
 }
 
-// Check the map read callback is called with UNKNOWN when the map request would have worked, but
-// Unmap was called
+// Check the map read callback is called with "UnmappedBeforeCallback" when the map request would
+// have worked, but Unmap was called
 TEST_F(WireBufferMappingTests, UnmapCalledTooEarlyForWrite) {
     wgpuBufferMapAsync(buffer, WGPUMapMode_Write, 0, kBufferSize, ToMockBufferMapCallback, nullptr);
 
@@ -341,7 +346,8 @@
     FlushClient();
 
     // Oh no! We are calling Unmap too early!
-    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _)).Times(1);
+    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback, _))
+        .Times(1);
     wgpuBufferUnmap(buffer);
 
     // The callback shouldn't get called, even when the request succeeded on the server side
diff --git a/src/tests/unittests/wire/WireMemoryTransferServiceTests.cpp b/src/tests/unittests/wire/WireMemoryTransferServiceTests.cpp
index cd8e6a2..7664de3 100644
--- a/src/tests/unittests/wire/WireMemoryTransferServiceTests.cpp
+++ b/src/tests/unittests/wire/WireMemoryTransferServiceTests.cpp
@@ -450,7 +450,8 @@
 
     // The server received a fatal failure and the client callback was never returned.
     // It is called when the wire is destructed.
-    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _)).Times(1);
+    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback, _))
+        .Times(1);
 
     EXPECT_CALL(clientMemoryTransferService, OnReadHandleDestroy(clientHandle)).Times(1);
 }
@@ -680,7 +681,8 @@
 
     // The server hit a fatal failure and never returned the callback. The client callback is
     // called when the wire is destructed.
-    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_Unknown, _)).Times(1);
+    EXPECT_CALL(*mockBufferMapCallback, Call(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback, _))
+        .Times(1);
 
     EXPECT_CALL(clientMemoryTransferService, OnWriteHandleDestroy(clientHandle)).Times(1);
 }