diff --git a/.changeset/close-position-path-only.md b/.changeset/close-position-path-only.md
new file mode 100644
index 00000000..f89aa468
--- /dev/null
+++ b/.changeset/close-position-path-only.md
@@ -0,0 +1,5 @@
+---
+"@0xmonaco/core": patch
+---
+
+Align close-position requests with the REST contract by keeping `position_id` in the URL path only.
diff --git a/packages/core/src/api/positions/api.ts b/packages/core/src/api/positions/api.ts
index 4677947e..e1b6a8b7 100644
--- a/packages/core/src/api/positions/api.ts
+++ b/packages/core/src/api/positions/api.ts
@@ -46,7 +46,6 @@ export class PositionsAPIImpl extends BaseAPI implements PositionsAPI {
     return await this.makeAuthenticatedRequest<ClosePositionResponse>(perpRoutes.positions.close(positionId), {
       method: "POST",
       body: JSON.stringify({
-        position_id: positionId,
         close_type: request.closeType,
         limit_price: request.limitPrice,
         slippage_tolerance_bps: request.slippageToleranceBps,
diff --git a/packages/core/tests/unit/api/positions.test.ts b/packages/core/tests/unit/api/positions.test.ts
index 4cfa874c..fe7db42e 100644
--- a/packages/core/tests/unit/api/positions.test.ts
+++ b/packages/core/tests/unit/api/positions.test.ts
@@ -87,7 +87,6 @@ describe("PositionsAPIImpl", () => {
         Authorization: `Bearer ${mockAccessToken}`,
       },
       body: JSON.stringify({
-        position_id: positionId,
         close_type: "LIMIT",
         limit_price: "50500",
         slippage_tolerance_bps: 100,