diff --git a/client/lib/wpcom-undocumented/lib/undocumented.js b/client/lib/wpcom-undocumented/lib/undocumented.js
index 50a6c724da460..7c79dfe465424 100644
--- a/client/lib/wpcom-undocumented/lib/undocumented.js
+++ b/client/lib/wpcom-undocumented/lib/undocumented.js
@@ -122,7 +122,7 @@ Undocumented.prototype.updateJetpackModuleSettings = function( siteId, moduleSlu
 	//@TODO: implement and test this endpoint, it's currently not working
 	return this.wpcom.req.post(
 		{ path: '/jetpack-blogs/' + siteId + '/rest-api/' },
-		{ path: '/module/' + moduleSlug, body: settings },
+		{ path: '/module/' + moduleSlug, body: JSON.stringify( settings ) },
 		fn
 	);
 };
diff --git a/client/state/jetpack-settings/module-settings/test/actions.js b/client/state/jetpack-settings/module-settings/test/actions.js
index 8fa2368d66fbd..9d4a8a4055670 100644
--- a/client/state/jetpack-settings/module-settings/test/actions.js
+++ b/client/state/jetpack-settings/module-settings/test/actions.js
@@ -107,7 +107,7 @@ describe( 'actions', () => {
 					.persist()
 					.post( '/rest/v1.1/jetpack-blogs/' + siteId + '/rest-api/', {
 						path: '/module/' + moduleSlug,
-						body: settings
+						body: JSON.stringify( settings )
 					} )
 					.reply( 200, {
 						code: 'success'
@@ -145,7 +145,7 @@ describe( 'actions', () => {
 					.persist()
 					.post( '/rest/v1.1/jetpack-blogs/' + siteId + '/rest-api/', {
 						path: '/module/' + moduleSlug,
-						body: settings
+						body: JSON.stringify( settings )
 					} )
 					.reply( 400, {
 						message: 'Invalid option: setting_1'