diff --git a/common/content/mappings.js b/common/content/mappings.js
index c39318f6..2c77c151 100644
--- a/common/content/mappings.js
+++ b/common/content/mappings.js
@@ -478,7 +478,7 @@ const Mappings = Module("mappings", {
                 return util.Array.flatten(
                 [
                     [[name, map.description] for ([i, name] in Iterator(map.names))]
-                    for ([i, map] in Iterator(this._user[mode].concat(this._main[mode])))
+                    for ([i, map] in Iterator(mappings._user[mode].concat(mappings._main[mode])))
                 ]);
             }
         ]);
diff --git a/common/content/style.js b/common/content/style.js
index 5223e25a..956ca82c 100644
--- a/common/content/style.js
+++ b/common/content/style.js
@@ -492,9 +492,9 @@ function Styles(name, store) {
      */
     this.removeSheet = function (system, name, filter, css, index) {
         let self = this;
-        if (arguments.length == 0) {
+        if (arguments.length == 1) {
             var matches = [system];
-            system = sheet.system;
+            system = matches[0].system;
         }
         let sheets = system ? systemSheets : userSheets;
         let names = system ? systemNames : userNames;