diff --git a/src/mcp/github-inline-comment-server.ts b/src/mcp/github-inline-comment-server.ts
index 28a8658..a432466 100644
--- a/src/mcp/github-inline-comment-server.ts
+++ b/src/mcp/github-inline-comment-server.ts
@@ -41,12 +41,14 @@ server.tool(
       ),
     line: z
       .number()
+      .nonnegative()
       .optional()
       .describe(
         "Line number for single-line comments (required if startLine is not provided)",
       ),
     startLine: z
       .number()
+      .nonnegative()
       .optional()
       .describe(
         "Start line for multi-line comments (use with line parameter for the end line)",