diff --git a/caps/include/nsPrincipalArray.h b/caps/include/nsPrincipalArray.h
index 7ec0df253a7..c9998151de4 100644
--- a/caps/include/nsPrincipalArray.h
+++ b/caps/include/nsPrincipalArray.h
@@ -14,7 +14,7 @@ NS_DECL_ISUPPORTS
 
 nsPrincipalArray(void);
 nsPrincipalArray(PRUint32 count);
-~nsPrincipalArray();
+virtual ~nsPrincipalArray();
 
 NS_IMETHOD
 ComparePrincipalArray(nsIPrincipalArray * other, PRInt16 * comparisonType);
diff --git a/xpcom/base/nsWeakReference.h b/xpcom/base/nsWeakReference.h
index 0d9e2a3a3ac..6a1b80542c7 100644
--- a/xpcom/base/nsWeakReference.h
+++ b/xpcom/base/nsWeakReference.h
@@ -14,7 +14,7 @@ class nsSupportsWeakReference : public nsISupportsWeakReference
 					// nothing else to do here
 				}
 
-			inline ~nsSupportsWeakReference();
+			inline virtual ~nsSupportsWeakReference();
 
 			NS_IMETHOD GetWeakReference( nsIWeakReference** );
 
@@ -54,7 +54,7 @@ class nsWeakReference : public nsIWeakReference
 					// nothing else to do here
 				}
 
-		 ~nsWeakReference()
+		virtual ~nsWeakReference()
 		 			// ...I will only be destroyed by calling |delete| myself.
 				{
 					if ( mReferent )
diff --git a/xpcom/glue/nsWeakReference.h b/xpcom/glue/nsWeakReference.h
index 0d9e2a3a3ac..6a1b80542c7 100644
--- a/xpcom/glue/nsWeakReference.h
+++ b/xpcom/glue/nsWeakReference.h
@@ -14,7 +14,7 @@ class nsSupportsWeakReference : public nsISupportsWeakReference
 					// nothing else to do here
 				}
 
-			inline ~nsSupportsWeakReference();
+			inline virtual ~nsSupportsWeakReference();
 
 			NS_IMETHOD GetWeakReference( nsIWeakReference** );
 
@@ -54,7 +54,7 @@ class nsWeakReference : public nsIWeakReference
 					// nothing else to do here
 				}
 
-		 ~nsWeakReference()
+		virtual ~nsWeakReference()
 		 			// ...I will only be destroyed by calling |delete| myself.
 				{
 					if ( mReferent )
diff --git a/xpfe/components/xfer/src/nsStreamXferOp.h b/xpfe/components/xfer/src/nsStreamXferOp.h
index 339dc103878..0e1348ff49c 100644
--- a/xpfe/components/xfer/src/nsStreamXferOp.h
+++ b/xpfe/components/xfer/src/nsStreamXferOp.h
@@ -43,7 +43,7 @@ class nsStreamXferOp : public nsIStreamTransferOperation,
 public:
     // ctor/dtor
     nsStreamXferOp( const nsString &source, const nsString &target );
-    ~nsStreamXferOp();
+    virtual ~nsStreamXferOp();
 
     // Implementation.
     NS_IMETHOD OpenDialog( nsIDOMWindow *parent );