diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 4084d0e44..85a0ccc90 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -1735,6 +1735,11 @@ void cmMakefile::AddDefinition(const char* name, bool value)
 #endif
 }
 
+void cmMakefile::MarkVariableAsUsed(const char* var)
+{
+  this->Internal->VarUsageStack.top().insert(var);
+}
+
 bool cmMakefile::VariableInitialized(const char* var) const
 {
   if(this->Internal->VarInitStack.top().find(var) != this->Internal->VarInitStack.top().end())
diff --git a/Source/cmMakefile.h b/Source/cmMakefile.h
index 89979d6a3..6b0bfa26a 100644
--- a/Source/cmMakefile.h
+++ b/Source/cmMakefile.h
@@ -61,6 +61,8 @@ public:
   unsigned int GetCacheMajorVersion();
   unsigned int GetCacheMinorVersion();
 
+  /* Mark a variable as used */
+  void MarkVariableAsUsed(const char* var);
   /* return true if a variable has been initialized */
   bool VariableInitialized(const char* ) const;
   /* return true if a variable has been used */