diff --git a/embedding/components/windowwatcher/public/nsIPromptService.idl b/embedding/components/windowwatcher/public/nsIPromptService.idl
index ab00a4fd5ffa..bfd6d98b3a94 100644
--- a/embedding/components/windowwatcher/public/nsIPromptService.idl
+++ b/embedding/components/windowwatcher/public/nsIPromptService.idl
@@ -52,7 +52,7 @@ interface nsIPromptService : nsISupports
                   in wstring dialogTitle,
                   in wstring text,
                   in wstring checkMsg,
-                  out boolean checkValue);
+                  inout boolean checkValue);
 
   /**
    * Puts up a dialog with OK and Cancel buttons.
@@ -71,7 +71,7 @@ interface nsIPromptService : nsISupports
                         in wstring dialogTitle,
                         in wstring text,
                         in wstring checkMsg,
-                        out boolean checkValue);
+                        inout boolean checkValue);
 
   /**
    * Puts up a dialog with up to 3 buttons and an optional checkbox.
diff --git a/netwerk/base/public/nsIPrompt.idl b/netwerk/base/public/nsIPrompt.idl
index 7dfac811ce79..4ae463c3011b 100644
--- a/netwerk/base/public/nsIPrompt.idl
+++ b/netwerk/base/public/nsIPrompt.idl
@@ -43,7 +43,7 @@ interface nsIPrompt : nsISupports
     void alertCheck(in wstring dialogTitle,
                     in wstring text,
                     in wstring checkMsg,
-                    out boolean checkValue);
+                    inout boolean checkValue);
 
     boolean confirm(in wstring dialogTitle,
                     in wstring text);
@@ -51,7 +51,7 @@ interface nsIPrompt : nsISupports
     boolean confirmCheck(in wstring dialogTitle,
                          in wstring text,
                          in wstring checkMsg,
-                         out boolean checkValue);
+                         inout boolean checkValue);
                          
     const unsigned long BUTTON_POS_0              = 1;
     const unsigned long BUTTON_POS_1              = 1 << 8;