diff --git a/src/mono/browser/build/BrowserWasmApp.targets b/src/mono/browser/build/BrowserWasmApp.targets
index 193e0db3d7286..4310617c9927b 100644
--- a/src/mono/browser/build/BrowserWasmApp.targets
+++ b/src/mono/browser/build/BrowserWasmApp.targets
@@ -271,6 +271,10 @@
       <WasmCompileOptimizationFlag>$(EmccCompileOptimizationFlag)</WasmCompileOptimizationFlag>
       <WasmBitcodeCompileOptimizationFlag Condition="'$(WasmBitcodeCompileOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</WasmBitcodeCompileOptimizationFlag>
       <WasmBitcodeCompileOptimizationFlag Condition="'$(WasmBitcodeCompileOptimizationFlag)' == '' ">$(WasmCompileOptimizationFlag)</WasmBitcodeCompileOptimizationFlag>
+
+      <!-- fixme https://github.com/WebAssembly/binaryen/issues/6639 -->
+      <EmccLinkOptimizationFlag Condition="$([MSBuild]::IsOSPlatform('windows'))">-O1</EmccLinkOptimizationFlag>
+
       <EmccLinkOptimizationFlag    Condition="'$(EmccLinkOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</EmccLinkOptimizationFlag>
       <EmccLinkOptimizationFlag    Condition="'$(EmccLinkOptimizationFlag)' == ''"   >$(WasmCompileOptimizationFlag)</EmccLinkOptimizationFlag>
       <WasmLinkOptimizationFlag>$(EmccLinkOptimizationFlag)</WasmLinkOptimizationFlag>
diff --git a/src/mono/wasm/build/WasmApp.Common.targets b/src/mono/wasm/build/WasmApp.Common.targets
index aae8ed7492fec..8df3969e45f56 100644
--- a/src/mono/wasm/build/WasmApp.Common.targets
+++ b/src/mono/wasm/build/WasmApp.Common.targets
@@ -501,7 +501,7 @@
       <WasmOptConfigurationFlags Include="@(_DefaulWasmOptConfigurationFlags)" />
 
       <!-- fixme: https://github.com/WebAssembly/binaryen/issues/6639 -->
-      <WasmOptConfigurationFlags Include="-O1" Condition="!$([MSBuild]::IsOSPlatform('windows'))" />
+      <WasmOptConfigurationFlags Include="-O1" Condition="$([MSBuild]::IsOSPlatform('windows'))" />
     </ItemGroup>
   </Target>