diff --git a/services/fxaccounts/FxAccounts.jsm b/services/fxaccounts/FxAccounts.jsm
index 4e665f8c6a44..b34957066665 100644
--- a/services/fxaccounts/FxAccounts.jsm
+++ b/services/fxaccounts/FxAccounts.jsm
@@ -653,7 +653,10 @@ FxAccountsInternal.prototype = {
   },
 
   _signOutServer: function signOutServer(sessionToken) {
-    return this.fxAccountsClient.signOut(sessionToken);
+    // For now we assume the service being logged out from is Sync - we might
+    // need to revisit this when this FxA code is used in a context that
+    // isn't Sync.
+    return this.fxAccountsClient.signOut(sessionToken, {service: "sync"});
   },
 
   /**
diff --git a/services/fxaccounts/FxAccountsClient.jsm b/services/fxaccounts/FxAccountsClient.jsm
index b65564231a21..dd5740f82a24 100644
--- a/services/fxaccounts/FxAccountsClient.jsm
+++ b/services/fxaccounts/FxAccountsClient.jsm
@@ -167,8 +167,12 @@ this.FxAccountsClient.prototype = {
    *        The session token encoded in hex
    * @return Promise
    */
-  signOut: function (sessionTokenHex) {
-    return this._request("/session/destroy", "POST",
+  signOut: function (sessionTokenHex, options = {}) {
+    let path = "/session/destroy";
+    if (options.service) {
+      path += "?service=" + options.service;
+    }
+    return this._request(path, "POST",
       deriveHawkCredentials(sessionTokenHex, "sessionToken"));
   },