diff --git a/Source/cmGeneratorExpression.cxx b/Source/cmGeneratorExpression.cxx
index 3ebb1b600..433adcf7c 100644
--- a/Source/cmGeneratorExpression.cxx
+++ b/Source/cmGeneratorExpression.cxx
@@ -33,17 +33,17 @@ cmGeneratorExpression::cmGeneratorExpression(
 cmsys::auto_ptr<cmCompiledGeneratorExpression>
 cmGeneratorExpression::Parse(std::string const& input)
 {
-  return this->Parse(input.c_str());
+  return cmsys::auto_ptr<cmCompiledGeneratorExpression>(
+                                      new cmCompiledGeneratorExpression(
+                                        this->Backtrace,
+                                        input));
 }
 
 //----------------------------------------------------------------------------
 cmsys::auto_ptr<cmCompiledGeneratorExpression>
 cmGeneratorExpression::Parse(const char* input)
 {
-  return cmsys::auto_ptr<cmCompiledGeneratorExpression>(
-                                      new cmCompiledGeneratorExpression(
-                                        this->Backtrace,
-                                        input));
+  return this->Parse(std::string(input ? input : ""));
 }
 
 cmGeneratorExpression::~cmGeneratorExpression()
@@ -122,13 +122,13 @@ const char *cmCompiledGeneratorExpression::Evaluate(
 
 cmCompiledGeneratorExpression::cmCompiledGeneratorExpression(
               cmListFileBacktrace const& backtrace,
-              const char *input)
-  : Backtrace(backtrace), Input(input ? input : ""),
+              const std::string& input)
+  : Backtrace(backtrace), Input(input),
     HadContextSensitiveCondition(false)
 {
   cmGeneratorExpressionLexer l;
   std::vector<cmGeneratorExpressionToken> tokens =
-                                              l.Tokenize(this->Input.c_str());
+                                              l.Tokenize(this->Input);
   this->NeedsEvaluation = l.GetSawGeneratorExpression();
 
   if (this->NeedsEvaluation)
diff --git a/Source/cmGeneratorExpression.h b/Source/cmGeneratorExpression.h
index 58abf1407..9aa590d36 100644
--- a/Source/cmGeneratorExpression.h
+++ b/Source/cmGeneratorExpression.h
@@ -100,7 +100,7 @@ public:
 
   ~cmCompiledGeneratorExpression();
 
-  std::string GetInput() const
+  std::string const& GetInput() const
   {
     return this->Input;
   }
@@ -116,7 +116,7 @@ public:
 
 private:
   cmCompiledGeneratorExpression(cmListFileBacktrace const& backtrace,
-              const char *input);
+              const std::string& input);
 
   friend class cmGeneratorExpression;
 
diff --git a/Source/cmGeneratorExpressionLexer.cxx b/Source/cmGeneratorExpressionLexer.cxx
index 117a24e09..1c83466ce 100644
--- a/Source/cmGeneratorExpressionLexer.cxx
+++ b/Source/cmGeneratorExpressionLexer.cxx
@@ -32,13 +32,11 @@ static void InsertText(const char *upto, const char *c,
 
 //----------------------------------------------------------------------------
 std::vector<cmGeneratorExpressionToken>
-cmGeneratorExpressionLexer::Tokenize(const char *input)
+cmGeneratorExpressionLexer::Tokenize(const std::string& input)
 {
   std::vector<cmGeneratorExpressionToken> result;
-  if (!input)
-    return result;
 
-  const char *c = input;
+  const char *c = input.c_str();
   const char *upto = c;
 
   for ( ; *c; ++c)
diff --git a/Source/cmGeneratorExpressionLexer.h b/Source/cmGeneratorExpressionLexer.h
index 83d661de1..1e2e8c25e 100644
--- a/Source/cmGeneratorExpressionLexer.h
+++ b/Source/cmGeneratorExpressionLexer.h
@@ -43,7 +43,7 @@ class cmGeneratorExpressionLexer
 public:
   cmGeneratorExpressionLexer();
 
-  std::vector<cmGeneratorExpressionToken> Tokenize(const char *input);
+  std::vector<cmGeneratorExpressionToken> Tokenize(const std::string& input);
 
   bool GetSawGeneratorExpression() const
   {