diff --git a/src/CodingWithCalvin.MCPServer.Server/CodingWithCalvin.MCPServer.Server.csproj b/src/CodingWithCalvin.MCPServer.Server/CodingWithCalvin.MCPServer.Server.csproj
index 430eee7..b6db853 100644
--- a/src/CodingWithCalvin.MCPServer.Server/CodingWithCalvin.MCPServer.Server.csproj
+++ b/src/CodingWithCalvin.MCPServer.Server/CodingWithCalvin.MCPServer.Server.csproj
@@ -20,7 +20,7 @@
     <PackageReference Include="StreamJsonRpc" Version="2.20.20" />
     <!-- Pin MessagePack above the transitive 2.5.187 pulled in by StreamJsonRpc to
          remediate GHSA-hv8m-jj95-wg3x (high severity, NU1903). -->
-    <PackageReference Include="MessagePack" Version="2.5.302" />
+    <PackageReference Include="MessagePack" Version="3.1.12" />
   </ItemGroup>
 
   <ItemGroup>