diff --git a/src/dawn_native/Toggles.cpp b/src/dawn_native/Toggles.cpp
index 8c7f33f..b0e2dea 100644
--- a/src/dawn_native/Toggles.cpp
+++ b/src/dawn_native/Toggles.cpp
@@ -225,6 +225,12 @@
               "be enabled for OpenGL ES backend, and serves as a workaround by default enabled on "
               "some Metal devices with Intel GPU to ensure the depth result is correct.",
               "https://crbug.com/dawn/136"}},
+            {Toggle::FxcOptimizations,
+             {"fxc_optimizations",
+              "Enable optimizations when compiling with FXC. Disabled by default because FXC "
+              "miscompiles in many cases when optimizations are enabled.",
+              "https://crbug.com/dawn/1203"}},
+
             // Dummy comment to separate the }} so it is clearer what to copy-paste to add a toggle.
         }};
     }  // anonymous namespace
diff --git a/src/dawn_native/Toggles.h b/src/dawn_native/Toggles.h
index 88a9d6d..4682cbd 100644
--- a/src/dawn_native/Toggles.h
+++ b/src/dawn_native/Toggles.h
@@ -60,6 +60,7 @@
         UseUserDefinedLabelsInBackend,
         DisableR8RG8Mipmaps,
         UseDummyFragmentInVertexOnlyPipeline,
+        FxcOptimizations,
 
         EnumCount,
         InvalidEnum = EnumCount,
diff --git a/src/dawn_native/d3d12/ComputePipelineD3D12.cpp b/src/dawn_native/d3d12/ComputePipelineD3D12.cpp
index dd8d225..b6037dd 100644
--- a/src/dawn_native/d3d12/ComputePipelineD3D12.cpp
+++ b/src/dawn_native/d3d12/ComputePipelineD3D12.cpp
@@ -34,6 +34,11 @@
         Device* device = ToBackend(GetDevice());
         uint32_t compileFlags = 0;
 
+        if (!device->IsToggleEnabled(Toggle::UseDXC) &&
+            !device->IsToggleEnabled(Toggle::FxcOptimizations)) {
+            compileFlags |= D3DCOMPILE_OPTIMIZATION_LEVEL0;
+        }
+
         if (device->IsToggleEnabled(Toggle::EmitHLSLDebugSymbols)) {
             compileFlags |= D3DCOMPILE_DEBUG | D3DCOMPILE_SKIP_OPTIMIZATION;
         }
diff --git a/src/dawn_native/d3d12/DeviceD3D12.cpp b/src/dawn_native/d3d12/DeviceD3D12.cpp
index 8eb4a87..a9bf033 100644
--- a/src/dawn_native/d3d12/DeviceD3D12.cpp
+++ b/src/dawn_native/d3d12/DeviceD3D12.cpp
@@ -518,10 +518,9 @@
         SetToggle(Toggle::UseD3D12ResidencyManagement, true);
         SetToggle(Toggle::UseDXC, false);
 
-#if defined(_DEBUG)
-        // Enable better shader debugging with the graphics debugging tools.
-        SetToggle(Toggle::EmitHLSLDebugSymbols, true);
-#endif
+        // Disable optimizations when using FXC
+        // See https://crbug.com/dawn/1203
+        SetToggle(Toggle::FxcOptimizations, false);
 
         // By default use the maximum shader-visible heap size allowed.
         SetToggle(Toggle::UseD3D12SmallShaderVisibleHeapForTesting, false);
diff --git a/src/dawn_native/d3d12/RenderPipelineD3D12.cpp b/src/dawn_native/d3d12/RenderPipelineD3D12.cpp
index dbe6252..de90d1d 100644
--- a/src/dawn_native/d3d12/RenderPipelineD3D12.cpp
+++ b/src/dawn_native/d3d12/RenderPipelineD3D12.cpp
@@ -326,6 +326,11 @@
         Device* device = ToBackend(GetDevice());
         uint32_t compileFlags = 0;
 
+        if (!device->IsToggleEnabled(Toggle::UseDXC) &&
+            !device->IsToggleEnabled(Toggle::FxcOptimizations)) {
+            compileFlags |= D3DCOMPILE_OPTIMIZATION_LEVEL0;
+        }
+
         if (device->IsToggleEnabled(Toggle::EmitHLSLDebugSymbols)) {
             compileFlags |= D3DCOMPILE_DEBUG | D3DCOMPILE_SKIP_OPTIMIZATION;
         }