diff --git a/CMakeLists.txt b/CMakeLists.txt
index d7686a8..e262b83 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -115,8 +115,13 @@ if(BUILD_TESTING)
     COMMAND tmux-mem-cpu-load --graph_lines -2
     )
 
+  add_test(NAME old_option_specification
+    COMMAND tmux-mem-cpu-load 2 8
+    )
+
   set_tests_properties(usage
     invalid_status_interval
     invalid_graph_lines
+    old_option_specification
     PROPERTIES WILL_FAIL TRUE)
 endif()
diff --git a/README.rst b/README.rst
index 9cf0128..90d885d 100644
--- a/README.rst
+++ b/README.rst
@@ -86,18 +86,34 @@ Edit ``$HOME/.tmux.conf`` to display the program's output in *status-left* or
 *status-right*.  For example::
 
   set -g status-interval 2
-  set -g status-left "#S #[fg=green,bg=black]#(tmux-mem-cpu-load --colors 2)#[default]"
+  set -g status-left "#S #[fg=green,bg=black]#(tmux-mem-cpu-load --colors --interval 2)#[default]"
 
-Note that the first argument to `tmux-mem-cpu-load` should be the same number
+Note that the *interval* argument to `tmux-mem-cpu-load` should be the same number
 of seconds that *status-interval* is set at.
 
-An optional second argument is the number of bars in the bar graph, which
+Another optional argument is the number of bars in the bar graph, which
 defaults to 10.  This can, for instance, be set to the number of cores in a
 multi-core system.
 
+The *colors* option will add graded colors for each of the measures.
 
-Author
-======
+The full usage::
+
+  Usage: tmux-mem-cpu-load [OPTIONS]
+
+  Available options:
+  -h, --help
+           Prints this help message
+  --colors
+          Use tmux colors in output
+  -i <value>, --interval <value>
+          Set tmux status refresh interval in seconds. Default: 1 second
+  -g <value>, --graph-lines <value>
+          Set how many lines should be drawn in a graph. Default: 10
+
+
+Authors
+=======
 
 Matt McCormick (thewtex) <matt@mmmccormick.com>
 
diff --git a/tmux-mem-cpu-load.cc b/tmux-mem-cpu-load.cc
index 737899a..2937a39 100644
--- a/tmux-mem-cpu-load.cc
+++ b/tmux-mem-cpu-load.cc
@@ -155,10 +155,18 @@ int main( int argc, char** argv )
         return EXIT_FAILURE;
         break;
       default:
-        std::cout << "?? getopt returned character code 0 " << c << std::endl;
+        std::cerr << "?? getopt returned character code 0 " << c << std::endl;
         return EXIT_FAILURE;
     }
   }
+  // Detect old option specification and return and error message.
+  if( argc > optind )
+  {
+    std::cout <<
+      "The interval and graph lines options are now specified with flags.\n\n";
+    print_help();
+    return EXIT_FAILURE;
+  }
 
   std::cout << mem_string( use_colors ) << ' '
     << cpu_string( cpu_usage_delay, graph_lines, use_colors ) << ' '