diff --git a/src/plugins/haskell/CMakeLists.txt b/src/plugins/haskell/CMakeLists.txt
index d45326695cb..6cd82f1109b 100644
--- a/src/plugins/haskell/CMakeLists.txt
+++ b/src/plugins/haskell/CMakeLists.txt
@@ -9,7 +9,7 @@ add_qtc_plugin(Haskell
     haskelleditorfactory.cpp haskelleditorfactory.h
     haskellhighlighter.cpp haskellhighlighter.h
     haskellmanager.cpp haskellmanager.h
-    haskellplugin.cpp haskellplugin.h
+    haskellplugin.cpp
     haskellproject.cpp haskellproject.h
     haskellrunconfiguration.cpp haskellrunconfiguration.h
     haskellsettings.cpp haskellsettings.h
diff --git a/src/plugins/haskell/haskell.qbs b/src/plugins/haskell/haskell.qbs
index 5c1be115387..d1362f32b11 100644
--- a/src/plugins/haskell/haskell.qbs
+++ b/src/plugins/haskell/haskell.qbs
@@ -18,7 +18,7 @@ QtcPlugin {
         "haskell_global.h",
         "haskellhighlighter.cpp", "haskellhighlighter.h",
         "haskellmanager.cpp", "haskellmanager.h",
-        "haskellplugin.cpp", "haskellplugin.h",
+        "haskellplugin.cpp",
         "haskellproject.cpp", "haskellproject.h",
         "haskellrunconfiguration.cpp", "haskellrunconfiguration.h",
         "haskellsettings.cpp", "haskellsettings.h",
diff --git a/src/plugins/haskell/haskellplugin.cpp b/src/plugins/haskell/haskellplugin.cpp
index 9c082c67a9e..80039b96b21 100644
--- a/src/plugins/haskell/haskellplugin.cpp
+++ b/src/plugins/haskell/haskellplugin.cpp
@@ -1,8 +1,6 @@
 // Copyright (c) 2017 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
 
-#include "haskellplugin.h"
-
 #include "haskellbuildconfiguration.h"
 #include "haskellconstants.h"
 #include "haskelleditorfactory.h"
@@ -16,6 +14,8 @@
 #include <coreplugin/editormanager/editormanager.h>
 #include <coreplugin/icore.h>
 
+#include <extensionsystem/iplugin.h>
+
 #include <projectexplorer/jsonwizard/jsonwizardfactory.h>
 #include <projectexplorer/projectmanager.h>
 #include <projectexplorer/runcontrol.h>
@@ -24,8 +24,7 @@
 
 #include <QAction>
 
-namespace Haskell {
-namespace Internal {
+namespace Haskell::Internal {
 
 class HaskellPluginPrivate
 {
@@ -37,11 +36,6 @@ public:
     ProjectExplorer::SimpleTargetRunnerFactory runWorkerFactory{{Constants::C_HASKELL_RUNCONFIG_ID}};
 };
 
-HaskellPlugin::~HaskellPlugin()
-{
-    delete d;
-}
-
 static void registerGhciAction(QObject *guard)
 {
     QAction *action = new QAction(Tr::tr("Run GHCi"), guard);
@@ -52,23 +46,32 @@ static void registerGhciAction(QObject *guard)
     });
 }
 
-bool HaskellPlugin::initialize(const QStringList &arguments, QString *errorString)
+class HaskellPlugin final : public ExtensionSystem::IPlugin
 {
-    Q_UNUSED(arguments)
-    Q_UNUSED(errorString)
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "Haskell.json")
 
-    d = new HaskellPluginPrivate;
+public:
+    ~HaskellPlugin() final { delete d; }
 
-    ProjectExplorer::ProjectManager::registerProjectType<HaskellProject>(
-        Constants::C_HASKELL_PROJECT_MIMETYPE);
-    TextEditor::SnippetProvider::registerGroup(Constants::C_HASKELLSNIPPETSGROUP_ID,
-                                               Tr::tr("Haskell", "SnippetProvider"));
+private:
+    void initialize() final
+    {
+        d = new HaskellPluginPrivate;
 
-    registerGhciAction(this);
+        ProjectExplorer::ProjectManager::registerProjectType<HaskellProject>(
+            Constants::C_HASKELL_PROJECT_MIMETYPE);
+        TextEditor::SnippetProvider::registerGroup(Constants::C_HASKELLSNIPPETSGROUP_ID,
+                                                   Tr::tr("Haskell", "SnippetProvider"));
 
-    ProjectExplorer::JsonWizardFactory::addWizardPath(":/haskell/share/wizards/");
-    return true;
-}
+        registerGhciAction(this);
 
-} // namespace Internal
-} // namespace Haskell
+        ProjectExplorer::JsonWizardFactory::addWizardPath(":/haskell/share/wizards/");
+    }
+
+    HaskellPluginPrivate *d = nullptr;
+};
+
+} // Haskell::Internal
+
+#include "haskellplugin.moc"
diff --git a/src/plugins/haskell/haskellplugin.h b/src/plugins/haskell/haskellplugin.h
deleted file mode 100644
index acae0d2001a..00000000000
--- a/src/plugins/haskell/haskellplugin.h
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright (c) 2017 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
-
-#pragma once
-
-#include "haskell_global.h"
-
-#include <extensionsystem/iplugin.h>
-
-namespace Haskell {
-namespace Internal {
-
-class HaskellPlugin : public ExtensionSystem::IPlugin
-{
-    Q_OBJECT
-    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "Haskell.json")
-
-public:
-    HaskellPlugin() = default;
-    ~HaskellPlugin() final;
-
-private:
-    bool initialize(const QStringList &arguments, QString *errorString) final;
-    void extensionsInitialized() final {}
-
-    class HaskellPluginPrivate *d = nullptr;
-};
-
-} // namespace Internal
-} // namespace Haskell