diff --git a/packages/opencode/src/mcp/index.ts b/packages/opencode/src/mcp/index.ts
index 045c58ef03..29e958fe35 100644
--- a/packages/opencode/src/mcp/index.ts
+++ b/packages/opencode/src/mcp/index.ts
@@ -135,7 +135,7 @@ export namespace MCP {
         return client.callTool(
           {
             name: mcpTool.name,
-            arguments: args as Record<string, unknown>,
+            arguments: (args || {}) as Record<string, unknown>,
           },
           CallToolResultSchema,
           {