diff --git a/Source/cmCacheManager.cxx b/Source/cmCacheManager.cxx
index bc2f0a794..2424526f0 100644
--- a/Source/cmCacheManager.cxx
+++ b/Source/cmCacheManager.cxx
@@ -190,8 +190,7 @@ bool cmCacheManager::IsOn(const char* key) const
     return false;
     }
   const std::string &v = m_Cache.find(key)->second.m_Value;
-  return (v == "ON" || v == "on" || v == "1" || v == "true" || v == "yev"
-          || v == "TRUE" || v == "True" || v == "y" || v == "Y");
+  return cmSystemTools::IsOn(v.c_str());
 }
 
 
diff --git a/Source/cmElseCommand.cxx b/Source/cmElseCommand.cxx
index ff396fc97..51e9f25c4 100644
--- a/Source/cmElseCommand.cxx
+++ b/Source/cmElseCommand.cxx
@@ -26,8 +26,7 @@ bool cmElseCommand::Invoke(std::vector<std::string>& args)
 
   // check to see if the argument is defined first
   const char *def = m_Makefile->GetDefinition(args[0].c_str());
-  if(def && strcmp(def,"0") && strcmp(def,"false") && strcmp(def,"") && 
-     strcmp(def,"NOTFOUND"))
+  if(cmSystemTools::IsOn(def))
     {
     // add block
     cmIfFunctionBlocker *f = new cmIfFunctionBlocker();
diff --git a/Source/cmIfCommand.cxx b/Source/cmIfCommand.cxx
index 5dab24b73..0701ee230 100644
--- a/Source/cmIfCommand.cxx
+++ b/Source/cmIfCommand.cxx
@@ -48,8 +48,7 @@ bool cmIfCommand::Invoke(std::vector<std::string>& args)
 
   // check to see if the argument is defined first
   const char *def = m_Makefile->GetDefinition(args[0].c_str());
-  if(def && strcmp(def,"0") && strcmp(def,"false") && strcmp(def,"") && 
-     strcmp(def,"NOTFOUND"))
+  if(cmSystemTools::IsOn(def))
     {
     // do nothing
     }
diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index 0087ca05d..2a27d3f02 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -18,6 +18,7 @@
 #include "stdio.h"
 #include <sys/stat.h>
 #include "cmRegularExpression.h"
+#include <ctype.h>
 
 #if defined(_MSC_VER) || defined(__BORLANDC__)
 #include <windows.h>
@@ -502,3 +503,19 @@ void cmSystemTools::RemoveFile(const char* source)
 {
   unlink(source);
 }
+
+bool cmSystemTools::IsOn(const char* val)
+{
+  if (!val)
+    {
+    return false;
+    }
+  std::basic_string<char> v = val;
+  
+  for(std::basic_string<char>::iterator c = v.begin();
+      c != v.end(); c++)
+    {
+    *c = toupper(*c);
+    }
+  return (v == "ON" || v == "1" || v == "YES" || v == "TRUE" || v == "Y");
+}
diff --git a/Source/cmSystemTools.h b/Source/cmSystemTools.h
index 04347fc4e..a13eb56ad 100644
--- a/Source/cmSystemTools.h
+++ b/Source/cmSystemTools.h
@@ -126,6 +126,8 @@ public:
   ///! Remove a file.
   static void RemoveFile(const char* source);
   
+  ///! does a string indicate a true or on value ?
+  static bool IsOn(const char* val);
   
   static long int ModifiedTime(const char* filename);