diff --git a/src/qml/EventHandlers/app.js b/src/qml/EventHandlers/app.js
index d026ada8..d199c65d 100644
--- a/src/qml/EventHandlers/app.js
+++ b/src/qml/EventHandlers/app.js
@@ -1,6 +1,8 @@
 // Copyright 2019 miruka
 // This file is part of harmonyqml, licensed under LGPLv3.
 
+"use strict"
+
 function onExitRequested(exitCode) {
     Qt.exit(exitCode)
 }
diff --git a/src/qml/EventHandlers/includes.js b/src/qml/EventHandlers/includes.js
index 4f56e77a..fd673974 100644
--- a/src/qml/EventHandlers/includes.js
+++ b/src/qml/EventHandlers/includes.js
@@ -1,6 +1,8 @@
 // Copyright 2019 miruka
 // This file is part of harmonyqml, licensed under LGPLv3.
 
+"use strict"
+
 // FIXME: Obsolete method, but need Qt 5.12+ for standard JS modules import
 Qt.include("app.js")
 Qt.include("users.js")
diff --git a/src/qml/EventHandlers/rooms.js b/src/qml/EventHandlers/rooms.js
index 241610a8..3ccf8aa4 100644
--- a/src/qml/EventHandlers/rooms.js
+++ b/src/qml/EventHandlers/rooms.js
@@ -1,6 +1,8 @@
 // Copyright 2019 miruka
 // This file is part of harmonyqml, licensed under LGPLv3.
 
+"use strict"
+
 Qt.include("../utils.js")
 
 function typingTextFor(members, ourUserId) {
diff --git a/src/qml/EventHandlers/users.js b/src/qml/EventHandlers/users.js
index c166812a..9d0c2f9a 100644
--- a/src/qml/EventHandlers/users.js
+++ b/src/qml/EventHandlers/users.js
@@ -1,6 +1,8 @@
 // Copyright 2019 miruka
 // This file is part of harmonyqml, licensed under LGPLv3.
 
+"use strict"
+
 function onAccountUpdated(userId) {
     accounts.append({userId})
 }
diff --git a/src/qml/utils.js b/src/qml/utils.js
index 2e403d95..7b6d2c52 100644
--- a/src/qml/utils.js
+++ b/src/qml/utils.js
@@ -1,6 +1,8 @@
 // Copyright 2019 miruka
 // This file is part of harmonyqml, licensed under LGPLv3.
 
+"use strict"
+
 
 function hsl(hue, saturation, lightness) {
     return hsla(hue, saturation, lightness)