diff --git a/src/mono/browser/browser.proj b/src/mono/browser/browser.proj
index e423a648c489b..a92061c0704f3 100644
--- a/src/mono/browser/browser.proj
+++ b/src/mono/browser/browser.proj
@@ -365,6 +365,9 @@
                                   $(ICULibDir)/libicudata.a;
                                   $(BrowserProjectRoot)runtime/hybrid-globalization/segmentation-rules.json" />
       <ICULibFiles Include="$(ICULibDir)/*.dat" />
+
+      <!-- fixme https://github.com/WebAssembly/binaryen/issues/6639 -->
+      <WasmOptConfigurationFlags Include="-O1" Condition="'$(OS)' == 'Windows_NT'" />
     </ItemGroup>
     <PropertyGroup>
       <PInvokeTableFile>$(ArtifactsObjDir)wasm/pinvoke-table.h</PInvokeTableFile>
@@ -382,6 +385,9 @@
       <CMakeConfigurationLinkFlags Condition="'$(WasmEnableThreads)' == 'true'">$(CMakeConfigurationLinkFlags) -Wno-pthreads-mem-growth</CMakeConfigurationLinkFlags>
       <CMakeConfigurationLinkFlags                                            >$(CMakeConfigurationLinkFlags) --emit-symbol-map</CMakeConfigurationLinkFlags>
 
+      <!-- fixme https://github.com/WebAssembly/binaryen/issues/6639 -->
+      <CMakeConfigurationLinkFlags Condition="'$(OS)' == 'Windows_NT'">$(CMakeConfigurationLinkFlags) -O1</CMakeConfigurationLinkFlags>
+
       <CMakeConfigurationEmsdkPath Condition="'$(Configuration)' == 'Release'"> -DEMSDK_PATH=&quot;$(EMSDK_PATH.TrimEnd('\/').Replace('\','/'))&quot;</CMakeConfigurationEmsdkPath>
 
       <CMakeBuildRuntimeConfigureCmd>emcmake cmake $(MSBuildThisFileDirectory)runtime</CMakeBuildRuntimeConfigureCmd>