diff --git a/docsrc/manual/scripting-capabilities.rst b/docsrc/manual/scripting-capabilities.rst
index 129159e4..6a48ab62 100644
--- a/docsrc/manual/scripting-capabilities.rst
+++ b/docsrc/manual/scripting-capabilities.rst
@@ -72,7 +72,7 @@ The grass-randomizer script above happens implicitly when the user paints on the
 
 .. code-block:: js
 
-	function applyNightTint() {
+	export function applyNightTint() {
 	    // Apply night palette tinting...
 	}
 
@@ -556,7 +556,7 @@ These are some miscellaneous functions that can be very useful when building cus
 
 .. js:function:: map.registerAction(functionName, actionName, shortcut = "")
 
-   Registers a JavaScript function to an action that can be manually triggered in Porymap's ``Tools`` menu. Optionally, a keyboard shortcut (e.g. ``"Ctrl+P"``) can also be specified, assuming it doesn't collide with any existing shortcuts used by Porymap.
+   Registers a JavaScript function to an action that can be manually triggered in Porymap's ``Tools`` menu. Optionally, a keyboard shortcut (e.g. ``"Ctrl+P"``) can also be specified, assuming it doesn't collide with any existing shortcuts used by Porymap. The function specified by ``functionName`` must have the ``export`` keyword.
 
    :param string functionName: name of the JavaScript function
    :param string actionName: name of the action that will be displayed in the ``Tools`` menu
diff --git a/include/scripting.h b/include/scripting.h
index 6f3b0d16..3e86f1b8 100644
--- a/include/scripting.h
+++ b/include/scripting.h
@@ -30,6 +30,7 @@ public:
     static void cb_ProjectClosed(QString projectPath);
     static void cb_MetatileChanged(int x, int y, Block prevBlock, Block newBlock);
     static void cb_MapOpened(QString mapName);
+    static bool tryErrorJS(QJSValue js);
 
 private:
     QJSEngine *engine;
diff --git a/src/mainwindow_scriptapi.cpp b/src/mainwindow_scriptapi.cpp
index 2084973e..20543c64 100644
--- a/src/mainwindow_scriptapi.cpp
+++ b/src/mainwindow_scriptapi.cpp
@@ -507,7 +507,7 @@ void MainWindow::setTimeout(QJSValue callback, int milliseconds) {
 }
 
 void MainWindow::invokeCallback(QJSValue callback) {
-    callback.call();
+    Scripting::tryErrorJS(callback.call());
 }
 
 void MainWindow::log(QString message) {
diff --git a/src/scripting.cpp b/src/scripting.cpp
index b14b0858..7879ea03 100644
--- a/src/scripting.cpp
+++ b/src/scripting.cpp
@@ -51,23 +51,25 @@ void Scripting::loadModules(QStringList moduleFiles) {
     }
 }
 
+bool Scripting::tryErrorJS(QJSValue js) {
+    if (!js.isError()) return false;
+
+    QFileInfo file(js.property("fileName").toString());
+    logError(QString("Error in custom script '%1' at line %2: '%3'")
+             .arg(file.fileName())
+             .arg(js.property("lineNumber").toString())
+             .arg(js.toString()));
+    return true;
+}
+
 void Scripting::invokeCallback(CallbackType type, QJSValueList args) {
     for (QJSValue module : this->modules) {
         QString functionName = callbackFunctions[type];
         QJSValue callbackFunction = module.property(functionName);
-        if (callbackFunction.isError()) {
-            continue;
-        }
+        if (tryErrorJS(callbackFunction)) continue;
 
         QJSValue result = callbackFunction.call(args);
-        if (result.isError()) {
-            QFileInfo file(result.property("fileName").toString());
-            logError(QString("Error in custom script '%1' at line %2: '%3'")
-                     .arg(file.fileName())
-                     .arg(result.property("lineNumber").toString())
-                     .arg(result.toString()));
-            continue;
-        }
+        if (tryErrorJS(result)) continue;
     }
 }
 
@@ -88,19 +90,14 @@ void Scripting::invokeAction(QString actionName) {
     QString functionName = instance->registeredActions.value(actionName);
     for (QJSValue module : instance->modules) {
         QJSValue callbackFunction = module.property(functionName);
-        if (callbackFunction.isError()) {
+        if (callbackFunction.isUndefined() || !callbackFunction.isCallable()) {
+            logError(QString("Unknown custom script function '%1'").arg(functionName));
             continue;
         }
+        if (tryErrorJS(callbackFunction)) continue;
 
         QJSValue result = callbackFunction.call(QJSValueList());
-        if (result.isError()) {
-            QFileInfo file(result.property("fileName").toString());
-            logError(QString("Error in custom script '%1' at line %2: '%3'")
-                     .arg(file.fileName())
-                     .arg(result.property("lineNumber").toString())
-                     .arg(result.toString()));
-            continue;
-        }
+        if (tryErrorJS(result)) continue;
     }
 }