diff --git a/src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs b/src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs
index f26e9ed5c..271b32b9d 100644
--- a/src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs
+++ b/src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs
@@ -1040,6 +1040,14 @@ internal static bool ValidateMcpHeaders(HttpContext context, JsonRpcMessage mess
             _ => null,
         };
         var mcpNameInBody = GetJsonNodeStringProperty(bodyParams, routingNameParameter);
+        if (mcpNameInBody is null &&
+            bodyParams is System.Text.Json.Nodes.JsonObject paramsObject &&
+            paramsObject.TryGetPropertyValue(routingNameParameter, out var routingNameNode) &&
+            routingNameNode is not null)
+        {
+            errorMessage = $"Header mismatch: body '{routingNameParameter}' value must be a string.";
+            return false;
+        }
 
         // Check that the header value matches the body value if the body value is present.
         if (!string.Equals(decodedMcpNameInHeader, mcpNameInBody, StringComparison.Ordinal))
@@ -1246,9 +1254,14 @@ argForMissing is not null &&
 
     private static string? GetJsonNodeStringProperty(System.Text.Json.Nodes.JsonNode? node, string propertyName)
     {
-        if (node is System.Text.Json.Nodes.JsonObject obj && obj.TryGetPropertyValue(propertyName, out var value))
-        {
-            return value?.GetValue<string>();
+        // A non-string value (number, bool, object, array) is a malformed request, not a server error,
+        // so report it as absent rather than letting GetValue<string>() throw.
+        if (node is System.Text.Json.Nodes.JsonObject obj &&
+            obj.TryGetPropertyValue(propertyName, out var value) &&
+            value is System.Text.Json.Nodes.JsonValue jsonValue &&
+            jsonValue.TryGetValue<string>(out var stringValue))
+        {
+            return stringValue;
         }
 
         return null;
diff --git a/tests/ModelContextProtocol.AspNetCore.Tests/HttpHeaderConformanceTests.cs b/tests/ModelContextProtocol.AspNetCore.Tests/HttpHeaderConformanceTests.cs
index 914b98db0..697e0a55d 100644
--- a/tests/ModelContextProtocol.AspNetCore.Tests/HttpHeaderConformanceTests.cs
+++ b/tests/ModelContextProtocol.AspNetCore.Tests/HttpHeaderConformanceTests.cs
@@ -297,6 +297,35 @@ public async Task Server_RejectsHeaderMismatch_WhenEmptyHeaderDoesNotMatchBody()
         Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
     }
 
+    [Theory]
+    [InlineData("tools/call", "name", "42")]
+    [InlineData("tools/call", "name", "true")]
+    [InlineData("tools/call", "name", "{}")]
+    [InlineData("tools/call", "name", "[]")]
+    [InlineData("prompts/get", "name", "42")]
+    [InlineData("resources/read", "uri", "{}")]
+    public async Task Server_RejectsNonStringRoutingNameInBody_WithJsonRpcError(string method, string routingParameter, string bodyValue)
+    {
+        await StartAsync();
+        await ProbeWithJuly2026ProtocolVersionAsync();
+
+        var callJson = "{\"jsonrpc\":\"2.0\",\"id\":77,\"method\":\"" + method + "\",\"params\":{\"" + routingParameter + "\":" + bodyValue +
+            @",""_meta"":{""io.modelcontextprotocol/protocolVersion"":""2026-07-28"",""io.modelcontextprotocol/clientInfo"":{""name"":""TestClient"",""version"":""1.0""},""io.modelcontextprotocol/clientCapabilities"":{}}}}";
+
+        using var request = new HttpRequestMessage(HttpMethod.Post, "");
+        request.Content = new StringContent(callJson, Encoding.UTF8, "application/json");
+        request.Headers.Add("MCP-Protocol-Version", "2026-07-28");
+        request.Headers.Add("Mcp-Method", method);
+        request.Headers.Add("Mcp-Name", "42");
+
+        using var response = await HttpClient.SendAsync(request, TestContext.Current.CancellationToken);
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+
+        var json = JsonNode.Parse(await response.Content.ReadAsStringAsync(TestContext.Current.CancellationToken))!;
+        Assert.Equal(77, json["id"]!.GetValue<int>());
+        Assert.Equal((int)McpErrorCode.HeaderMismatch, json["error"]!["code"]!.GetValue<int>());
+    }
+
     [Fact]
     public async Task Server_AcceptsBase64EncodedHeaderWithControlChars()
     {