diff --git a/src/Polyfill/Polyfill.targets b/src/Polyfill/Polyfill.targets
index 3b785a66..f456d5f7 100644
--- a/src/Polyfill/Polyfill.targets
+++ b/src/Polyfill/Polyfill.targets
@@ -56,6 +56,7 @@
     </PropertyGroup>
     <PropertyGroup>
       <DefineConstants Condition="$(MemoryReferenced)">$(DefineConstants);HAS_SPAN</DefineConstants>
+      <DefineConstants Condition="$(LowerFramework.StartsWith('net9'))">$(DefineConstants);HAS_SPAN</DefineConstants>
       <DefineConstants Condition="$(LowerFramework.StartsWith('net8'))">$(DefineConstants);HAS_SPAN</DefineConstants>
       <DefineConstants Condition="$(LowerFramework.StartsWith('net7'))">$(DefineConstants);HAS_SPAN</DefineConstants>
       <DefineConstants Condition="$(LowerFramework.StartsWith('net6'))">$(DefineConstants);HAS_SPAN</DefineConstants>