diff --git a/widget/nsIWidget.h b/widget/nsIWidget.h
index fceaff168e40..dac93db2d841 100644
--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -244,7 +244,7 @@ struct nsIMEUpdatePreference {
   {
   }
 
-  nsIMEUpdatePreference(Notifications aWantUpdates)
+  explicit nsIMEUpdatePreference(Notifications aWantUpdates)
     : mWantUpdates(aWantUpdates | DEFAULT_CONDITIONS_OF_NOTIFYING_CHANGES)
   {
   }
@@ -369,7 +369,7 @@ struct IMEState {
 
   IMEState() : mEnabled(ENABLED), mOpen(DONT_CHANGE_OPEN_STATE) { }
 
-  IMEState(Enabled aEnabled, Open aOpen = DONT_CHANGE_OPEN_STATE) :
+  explicit IMEState(Enabled aEnabled, Open aOpen = DONT_CHANGE_OPEN_STATE) :
     mEnabled(aEnabled), mOpen(aOpen)
   {
   }
@@ -452,8 +452,8 @@ struct InputContextAction {
   {
   }
 
-  InputContextAction(Cause aCause,
-                     FocusChange aFocusChange = FOCUS_NOT_CHANGED) :
+  explicit InputContextAction(Cause aCause,
+                              FocusChange aFocusChange = FOCUS_NOT_CHANGED) :
     mCause(aCause), mFocusChange(aFocusChange)
   {
   }
@@ -510,7 +510,7 @@ enum IMEMessage MOZ_ENUM_TYPE(int8_t)
 
 struct IMENotification
 {
-  IMENotification(IMEMessage aMessage)
+  MOZ_IMPLICIT IMENotification(IMEMessage aMessage)
     : mMessage(aMessage)
   {
     switch (aMessage) {
diff --git a/widget/xpwidgets/GfxInfoCollector.h b/widget/xpwidgets/GfxInfoCollector.h
index c4c1a618ee1e..66c35fe96722 100644
--- a/widget/xpwidgets/GfxInfoCollector.h
+++ b/widget/xpwidgets/GfxInfoCollector.h
@@ -29,7 +29,7 @@ class MOZ_STACK_CLASS InfoObject
 
   private:
   // We need to ensure that this object lives on the stack so that GC sees it properly
-  InfoObject(JSContext *aCx);
+  explicit InfoObject(JSContext *aCx);
   InfoObject(InfoObject&);
 
   JSContext *mCx;