diff --git a/scripts/process_function_template.py b/scripts/process_function_template.py
index 6e1fdf77051..c8cf87df3a6 100644
--- a/scripts/process_function_template.py
+++ b/scripts/process_function_template.py
@@ -13,12 +13,11 @@ sys.path.append(
 cpp = open(sys.argv[1], "w", encoding="utf-8")
 cpp.write(
     "#include \"qgsexpression.h\"\n"
-    "\n"
-    "QHash<QString, QgsExpression::Help> QgsExpression::sFunctionHelpTexts;\n"
+    "#include \"qgsexpression_p.h\"\n"
     "\n"
     "void QgsExpression::initFunctionHelp()\n"
     "{\n"
-    "  if( !sFunctionHelpTexts.isEmpty() )\n"
+    "  if( !sFunctionHelpTexts()->isEmpty() )\n"
     "    return;"
 )
 
@@ -77,7 +76,7 @@ for f in sorted(glob.glob('resources/function_help/json/*')):
             if len(list(v['arguments'])) < 1 or len(list(v['arguments'])) > 2:
                 raise BaseException("%s: 1 or 2 arguments expected for operator")
 
-    cpp.write("\n\n  sFunctionHelpTexts.insert( {0},\n    Help( {0}, tr( \"{1}\" ), tr( \"{2}\" ),\n      QList<HelpVariant>()".format(
+    cpp.write("\n\n  sFunctionHelpTexts()->insert( {0},\n    Help( {0}, tr( \"{1}\" ), tr( \"{2}\" ),\n      QList<HelpVariant>()".format(
         name, json_params['type'], json_params['description'])
     )
 
@@ -121,7 +120,7 @@ for f in sorted(glob.glob('resources/function_help/text/*')):
     n = os.path.basename(f)
 
     with open(f) as content:
-        cpp.write("\n\n  sFunctionHelpTexts.insert( \"{0}\",\n    Help( tr( \"{0}\" ), tr( \"group\" ), tr( \"{1}\" ), QList<HelpVariant>() ) );\n".format(
+        cpp.write("\n\n  sFunctionHelpTexts()->insert( \"{0}\",\n    Help( tr( \"{0}\" ), tr( \"group\" ), tr( \"{1}\" ), QList<HelpVariant>() ) );\n".format(
             n, content.read().replace("\\", "&#92;").replace('\\', '\\\\').replace('"', '\\"').replace('\n', '\\n')))
 
 cpp.write("\n}\n")
diff --git a/src/core/expression/qgsexpression.cpp b/src/core/expression/qgsexpression.cpp
index 60b7568e659..587dcffdf29 100644
--- a/src/core/expression/qgsexpression.cpp
+++ b/src/core/expression/qgsexpression.cpp
@@ -24,89 +24,11 @@
 #include "qgsgeometry.h"
 #include "qgsproject.h"
 #include "qgsexpressioncontextutils.h"
+#include "qgsexpression_p.h"
 
 // from parser
 extern QgsExpressionNode *parseExpression( const QString &str, QString &parserErrorMsg, QList<QgsExpression::ParserError> &parserErrors );
 
-
-struct HelpArg
-{
-  HelpArg( const QString &arg, const QString &desc, bool descOnly = false, bool syntaxOnly = false,
-           bool optional = false, const QString &defaultVal = QString() )
-    : mArg( arg )
-    , mDescription( desc )
-    , mDescOnly( descOnly )
-    , mSyntaxOnly( syntaxOnly )
-    , mOptional( optional )
-    , mDefaultVal( defaultVal )
-  {}
-
-  QString mArg;
-  QString mDescription;
-  bool mDescOnly;
-  bool mSyntaxOnly;
-  bool mOptional;
-  QString mDefaultVal;
-};
-
-struct HelpExample
-{
-  HelpExample( const QString &expression, const QString &returns, const QString &note = QString() )
-    : mExpression( expression )
-    , mReturns( returns )
-    , mNote( note )
-  {}
-
-  QString mExpression;
-  QString mReturns;
-  QString mNote;
-};
-
-
-struct HelpVariant
-{
-  HelpVariant( const QString &name, const QString &description,
-               const QList<HelpArg> &arguments = QList<HelpArg>(),
-               bool variableLenArguments = false,
-               const QList<HelpExample> &examples = QList<HelpExample>(),
-               const QString &notes = QString() )
-    : mName( name )
-    , mDescription( description )
-    , mArguments( arguments )
-    , mVariableLenArguments( variableLenArguments )
-    , mExamples( examples )
-    , mNotes( notes )
-  {}
-
-  QString mName;
-  QString mDescription;
-  QList<HelpArg> mArguments;
-  bool mVariableLenArguments;
-  QList<HelpExample> mExamples;
-  QString mNotes;
-};
-
-
-struct Help
-{
-  //! Constructor for expression help
-  Help() = default;
-
-  Help( const QString &name, const QString &type, const QString &description, const QList<HelpVariant> &variants )
-    : mName( name )
-    , mType( type )
-    , mDescription( description )
-    , mVariants( variants )
-  {}
-
-  QString mName;
-  QString mType;
-  QString mDescription;
-  QList<HelpVariant> mVariants;
-};
-
-typedef QHash<QString, Help> HelpTextHash;
-Q_GLOBAL_STATIC( HelpTextHash, sFunctionHelpTexts )
 Q_GLOBAL_STATIC( QgsStringMap, sVariableHelpTexts )
 Q_GLOBAL_STATIC( QgsStringMap, sGroups )
 
diff --git a/src/core/expression/qgsexpression_p.h b/src/core/expression/qgsexpression_p.h
new file mode 100644
index 00000000000..26279995f68
--- /dev/null
+++ b/src/core/expression/qgsexpression_p.h
@@ -0,0 +1,111 @@
+/***************************************************************************
+     qgsexpression_p.h
+     ---------------
+    Date                 : October 2019
+    Copyright            : (C) 2019 by Matthias Kuhn
+    Email                : matthias@opengis.ch
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#ifndef QGSEXPRESSIONPRIVATE_H
+#define QGSEXPRESSIONPRIVATE_H
+
+/// @cond PRIVATE
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the QGIS API.  It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+
+#define SIP_NO_FILE
+
+#include "qgsexpression.h"
+
+struct HelpArg
+{
+  HelpArg( const QString &arg, const QString &desc, bool descOnly = false, bool syntaxOnly = false,
+           bool optional = false, const QString &defaultVal = QString() )
+    : mArg( arg )
+    , mDescription( desc )
+    , mDescOnly( descOnly )
+    , mSyntaxOnly( syntaxOnly )
+    , mOptional( optional )
+    , mDefaultVal( defaultVal )
+  {}
+
+  QString mArg;
+  QString mDescription;
+  bool mDescOnly;
+  bool mSyntaxOnly;
+  bool mOptional;
+  QString mDefaultVal;
+};
+
+struct HelpExample
+{
+  HelpExample( const QString &expression, const QString &returns, const QString &note = QString() )
+    : mExpression( expression )
+    , mReturns( returns )
+    , mNote( note )
+  {}
+
+  QString mExpression;
+  QString mReturns;
+  QString mNote;
+};
+
+
+struct HelpVariant
+{
+  HelpVariant( const QString &name, const QString &description,
+               const QList<HelpArg> &arguments = QList<HelpArg>(),
+               bool variableLenArguments = false,
+               const QList<HelpExample> &examples = QList<HelpExample>(),
+               const QString &notes = QString() )
+    : mName( name )
+    , mDescription( description )
+    , mArguments( arguments )
+    , mVariableLenArguments( variableLenArguments )
+    , mExamples( examples )
+    , mNotes( notes )
+  {}
+
+  QString mName;
+  QString mDescription;
+  QList<HelpArg> mArguments;
+  bool mVariableLenArguments;
+  QList<HelpExample> mExamples;
+  QString mNotes;
+};
+
+
+struct Help
+{
+  //! Constructor for expression help
+  Help() = default;
+
+  Help( const QString &name, const QString &type, const QString &description, const QList<HelpVariant> &variants )
+    : mName( name )
+    , mType( type )
+    , mDescription( description )
+    , mVariants( variants )
+  {}
+
+  QString mName;
+  QString mType;
+  QString mDescription;
+  QList<HelpVariant> mVariants;
+};
+
+typedef QHash<QString, Help> HelpTextHash;
+Q_GLOBAL_STATIC( HelpTextHash, sFunctionHelpTexts )
+#endif // QGSEXPRESSIONPRIVATE_H