diff --git a/lib/rscons/cache.rb b/lib/rscons/cache.rb
index 14acaa4..a336ca2 100644
--- a/lib/rscons/cache.rb
+++ b/lib/rscons/cache.rb
@@ -2,33 +2,37 @@ require 'yaml'
 require 'fileutils'
 require 'digest/md5'
 require 'set'
+require 'rscons/version'
 
 module Rscons
   # Example cache:
   # {
-  #   'program' => {
-  #     'checksum' => 'A1B2C3D4',
-  #     'command' => ['gcc', '-o', 'program', 'program.o'],
-  #     'deps' => [
-  #       {
-  #         'fname' => 'program.o',
-  #         'checksum' => '87654321',
-  #       }
-  #     ],
-  #   }
-  #   'program.o' => {
-  #     'checksum' => '87654321',
-  #     'command' => ['gcc', '-c', '-o', 'program.o', 'program.c'],
-  #     'deps' => [
-  #       {
-  #         'fname' => 'program.c',
-  #         'checksum' => '456789ABC',
-  #       },
-  #       {
-  #         'fname' => 'program.h',
-  #         'checksum' => '7979764643',
-  #       }
-  #     ]
+  #   version: '1.2.3',
+  #   targets: {
+  #     'program' => {
+  #       'checksum' => 'A1B2C3D4',
+  #       'command' => ['gcc', '-o', 'program', 'program.o'],
+  #       'deps' => [
+  #         {
+  #           'fname' => 'program.o',
+  #           'checksum' => '87654321',
+  #         }
+  #       ],
+  #     }
+  #     'program.o' => {
+  #       'checksum' => '87654321',
+  #       'command' => ['gcc', '-c', '-o', 'program.o', 'program.c'],
+  #       'deps' => [
+  #         {
+  #           'fname' => 'program.c',
+  #           'checksum' => '456789ABC',
+  #         },
+  #         {
+  #           'fname' => 'program.h',
+  #           'checksum' => '7979764643',
+  #         }
+  #       ]
+  #     }
   #   }
   # }
   class Cache
@@ -42,7 +46,10 @@ module Rscons
 
     # Instance Methods
     def initialize
-      @cache = YAML.load(File.read(CACHE_FILE)) rescue {}
+      @cache = YAML.load(File.read(CACHE_FILE)) rescue {
+        targets: {},
+        version: VERSION,
+      }
       @lookup_checksums = {}
     end
 
@@ -57,12 +64,12 @@ module Rscons
       return false unless File.exists?(target)
 
       # target must be registered in the cache
-      return false unless @cache.has_key?(target)
+      return false unless @cache[:targets].has_key?(target)
 
       # command used to build target must be identical
-      return false unless @cache[target][:command] == command
+      return false unless @cache[:targets][target][:command] == command
 
-      cached_deps = @cache[target][:deps].map { |dc| dc[:fname] }
+      cached_deps = @cache[:targets][target][:deps].map { |dc| dc[:fname] }
       if options[:strict_deps]
         # depedencies passed in must exactly equal those in the cache
         return false unless deps == cached_deps
@@ -72,13 +79,13 @@ module Rscons
       end
 
       # all cached dependencies must have their checksums match
-      @cache[target][:deps].map do |dep_cache|
+      @cache[:targets][target][:deps].map do |dep_cache|
         dep_cache[:checksum] == lookup_checksum(dep_cache[:fname])
       end.all?
     end
 
     def register_build(target, command, deps)
-      @cache[target] = {
+      @cache[:targets][target] = {
         command: command,
         checksum: calculate_checksum(target),
         deps: deps.map do |dep|