diff --git a/src/RESTDataSource.ts b/src/RESTDataSource.ts
index 6581f1a..da83bd7 100644
--- a/src/RESTDataSource.ts
+++ b/src/RESTDataSource.ts
@@ -228,7 +228,9 @@ export abstract class RESTDataSource {
       } else if (!modifiedRequest.headers['content-type']) {
         modifiedRequest.headers['content-type'] = 'application/json';
       }
-    }
+    } else if (typeof request.body === 'string') {
+      modifiedRequest.body = request.body;
+    } 
 
     if (this.willSendRequest) {
       await this.willSendRequest(modifiedRequest);