diff --git a/python/core/__init__.py b/python/core/__init__.py
index f0ff94e110c..1f9468b9db8 100644
--- a/python/core/__init__.py
+++ b/python/core/__init__.py
@@ -112,7 +112,7 @@ def register_function(function, arg_count, group, usesgeometry=False,
 
     helptemplate = string.Template("""<h3>$name function</h3><br>$doc""")
     name = kwargs.get('name', function.__name__)
-    helptext = function.__doc__ or ''
+    helptext = kwargs.get('helpText') or function.__doc__ or ''
     helptext = helptext.strip()
     expandargs = False
 
diff --git a/tests/src/python/test_qgsexpression.py b/tests/src/python/test_qgsexpression.py
index 67efbd99762..af318eef797 100644
--- a/tests/src/python/test_qgsexpression.py
+++ b/tests/src/python/test_qgsexpression.py
@@ -43,6 +43,18 @@ class TestQgsExpressionCustomFunctions(unittest.TestCase):
     def sqrt(values, feature, parent):
         pass
 
+    @qgsfunction(1, 'testing', register=False)
+    def help_with_docstring(values, feature, parent):
+        """The help comes from the python docstring."""
+        pass
+
+    help_text = 'The help comes from a variable.'
+
+    @qgsfunction(1, 'testing', register=False, helpText=help_text)
+    def help_with_variable(values, feature, parent):
+        """This docstring is not used for the help."""
+        pass
+
     @qgsfunction(1, 'testing', register=False, usesgeometry=True)
     def geomtest(values, feature, parent):
         pass
@@ -68,6 +80,17 @@ class TestQgsExpressionCustomFunctions(unittest.TestCase):
         args = function.params()
         self.assertEqual(args, 3)
 
+    def testHelp(self):
+        QgsExpression.registerFunction(self.help_with_variable)
+        html = ('<h3>help_with_variable function</h3><br>'
+                'The help comes from a variable.')
+        self.assertEqual(self.help_with_variable.helpText(), html)
+
+        QgsExpression.registerFunction(self.help_with_docstring)
+        html = ('<h3>help_with_docstring function</h3><br>'
+                'The help comes from the python docstring.')
+        self.assertEqual(self.help_with_docstring.helpText(), html)
+
     def testAutoArgsAreExpanded(self):
         function = self.expandargs
         args = function.params()