diff --git a/.changeset/zod-elicit-compat.md b/.changeset/zod-elicit-compat.md
new file mode 100644
index 000000000..5274b825f
--- /dev/null
+++ b/.changeset/zod-elicit-compat.md
@@ -0,0 +1,5 @@
+---
+"@modelcontextprotocol/core": patch
+---
+
+Allow `$schema` and `additionalProperties` in elicitation `requestedSchema` for Zod `.toJSONSchema()` compatibility
diff --git a/packages/core/src/types/schemas.ts b/packages/core/src/types/schemas.ts
index 309b6ade2..dba423361 100644
--- a/packages/core/src/types/schemas.ts
+++ b/packages/core/src/types/schemas.ts
@@ -1862,9 +1862,11 @@ export const ElicitRequestFormParamsSchema = TaskAugmentedRequestParamsSchema.ex
      * Only top-level properties are allowed, without nesting.
      */
     requestedSchema: z.object({
+        $schema: z.string().optional(),
         type: z.literal('object'),
         properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
-        required: z.array(z.string()).optional()
+        required: z.array(z.string()).optional(),
+        additionalProperties: z.boolean().optional()
     })
 });
 
diff --git a/packages/core/src/types/spec.types.ts b/packages/core/src/types/spec.types.ts
index ba849c546..6e35eaaea 100644
--- a/packages/core/src/types/spec.types.ts
+++ b/packages/core/src/types/spec.types.ts
@@ -1740,6 +1740,7 @@ export interface Tool extends BaseMetadata, Icons {
         type: 'object';
         properties?: { [key: string]: JSONValue };
         required?: string[];
+        additionalProperties?: boolean;
     };
 
     /**
@@ -1759,6 +1760,7 @@ export interface Tool extends BaseMetadata, Icons {
         type: 'object';
         properties?: { [key: string]: JSONValue };
         required?: string[];
+        additionalProperties?: boolean;
     };
 
     /**
@@ -2801,6 +2803,7 @@ export interface ElicitRequestFormParams extends TaskAugmentedRequestParams {
             [key: string]: PrimitiveSchemaDefinition;
         };
         required?: string[];
+        additionalProperties?: boolean;
     };
 }