diff --git a/include/llvm/Function.h b/include/llvm/Function.h
index 4c0e0ec5235..87e6bad48a3 100644
--- a/include/llvm/Function.h
+++ b/include/llvm/Function.h
@@ -85,7 +85,7 @@ public:
   /// is empty if so) this is true for external functions, defined as forward
   /// "declare"ations
   ///
-  bool isExternal() const { return BasicBlocks.empty(); }
+  virtual bool isExternal() const { return BasicBlocks.empty(); }
 
   // getNext/Prev - Return the next or previous function in the list.  These
   // methods should never be used directly, and are only used to implement the
diff --git a/include/llvm/GlobalValue.h b/include/llvm/GlobalValue.h
index 56e4a3e28a1..af2ff23c82e 100644
--- a/include/llvm/GlobalValue.h
+++ b/include/llvm/GlobalValue.h
@@ -26,17 +26,22 @@ protected:
 public:
   ~GlobalValue() {}
 
-  // getType - Global values are always pointers.
+  /// getType - Global values are always pointers.
   inline const PointerType *getType() const {
     return (const PointerType*)User::getType();
   }
 
-  // Internal Linkage - True if the global value is inaccessible to 
+  /// Internal Linkage - True if the global value is inaccessible to 
   bool hasInternalLinkage() const { return HasInternalLinkage; }
   bool hasExternalLinkage() const { return !HasInternalLinkage; }
   void setInternalLinkage(bool HIL) { HasInternalLinkage = HIL; }
 
-  // Get the module that this global value is contained inside of...
+  /// isExternal - Return true if the primary definition of this global value is
+  /// outside of the current translation unit...
+  virtual bool isExternal() const = 0;
+
+  /// getParent - Get the module that this global value is contained inside
+  /// of...
   inline Module *getParent() { return Parent; }
   inline const Module *getParent() const { return Parent; }
 
diff --git a/include/llvm/GlobalVariable.h b/include/llvm/GlobalVariable.h
index 12862cc4f66..372b7a25e66 100644
--- a/include/llvm/GlobalVariable.h
+++ b/include/llvm/GlobalVariable.h
@@ -46,7 +46,7 @@ public:
   /// global variable is defined in some other translation unit, and is thus
   /// externally defined here.
   ///
-  bool isExternal() const { return Operands.empty(); }
+  virtual bool isExternal() const { return Operands.empty(); }
 
   /// hasInitializer - Unless a global variable isExternal(), it has an
   /// initializer.  The initializer for the global variable/constant is held by