diff --git a/src/ApiBuilderTests/AssemblySizeTest.cs b/src/ApiBuilderTests/AssemblySizeTest.cs
index bb00ea5d..cd89091f 100644
--- a/src/ApiBuilderTests/AssemblySizeTest.cs
+++ b/src/ApiBuilderTests/AssemblySizeTest.cs
@@ -164,7 +164,7 @@ public void MeasureAssemblySizes()
                           {polyOptions}
                         </PropertyGroup>
                         <ItemGroup>
-                          <PackageReference Include="System.Memory" Condition="'$(TargetFrameworkIdentifier)' == '.NETStandard' or '$(TargetFrameworkIdentifier)' == '.NETFramework' or $(TargetFramework.StartsWith('netcoreapp'))" Version="4.5.5" />
+                          <PackageReference Include="System.Memory" Condition="'$(TargetFrameworkIdentifier)' == '.NETStandard' or '$(TargetFrameworkIdentifier)' == '.NETFramework' or $(TargetFramework.StartsWith('netcoreapp'))" Version="4.5.4" />
                           <PackageReference Include="System.ValueTuple" Condition="$(TargetFramework.StartsWith('net46'))" Version="4.5.0" />
                           <PackageReference Include="System.Net.Http" Condition="$(TargetFramework.StartsWith('net4'))" Version="4.3.4" />
                           <PackageReference Include="System.Threading.Tasks.Extensions" Condition="'$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netcoreapp2.0' or '$(TargetFrameworkIdentifier)' == '.NETFramework'" Version="4.5.4" />
@@ -335,4 +335,4 @@ class SizeResult
         public long SizeWithStringInterpolation { get; init; }
         public long SizeWithNullability { get; init; }
     }
-}
\ No newline at end of file
+}
diff --git a/src/Polyfill/Polyfill.targets b/src/Polyfill/Polyfill.targets
index 5ac19a8f..27c44283 100644
--- a/src/Polyfill/Polyfill.targets
+++ b/src/Polyfill/Polyfill.targets
@@ -88,7 +88,7 @@ For example:
       <MemoryVersion>@(ResolvedCompileFileDefinitions->WithMetadataValue('NuGetPackageId', 'System.Memory')->Metadata('NuGetPackageVersion'))</MemoryVersion>
       
       <DefineConstants
-        Condition="'$(MemoryVersion)' != '' AND $([MSBuild]::VersionGreaterThanOrEquals($(MemoryVersion), '4.5.5'))">$(DefineConstants);FeatureMemory</DefineConstants>
+        Condition="'$(MemoryVersion)' != '' AND $([MSBuild]::VersionGreaterThanOrEquals($(MemoryVersion), '4.5.4'))">$(DefineConstants);FeatureMemory</DefineConstants>
       
       <DefineConstants
         Condition="@(ResolvedCompileFileDefinitions->AnyHaveMetadataValue('NuGetPackageId', 'System.Runtime.InteropServices.RuntimeInformation'))">$(DefineConstants);FeatureRuntimeInformation</DefineConstants>