diff --git a/bin/cheat b/bin/cheat
index 0e7fb7c..08ccaa6 100755
--- a/bin/cheat
+++ b/bin/cheat
@@ -37,10 +37,24 @@ Examples:
 # require the dependencies
 from cheat import sheets, sheet
 from cheat.utils import colorize
+from cheat.utils import die
 from docopt import docopt
+import os
 
 
 if __name__ == '__main__':
+
+    # validate CHEAT_HIGHLIGHT values if set
+    colors = [
+        'grey' , 'red'     , 'green' , 'yellow' ,
+        'blue' , 'magenta' , 'cyan'  , 'white'  ,
+    ]
+    if (
+        os.environ.get('CHEAT_HIGHLIGHT') and
+        os.environ.get('CHEAT_HIGHLIGHT') not in colors
+    ):
+        die("%s %s" %('CHEAT_HIGHLIGHT must be one of:', colors))
+
     # parse the command-line options
     options = docopt(__doc__, version='cheat 2.3.1')