diff --git a/lib/lrucache.rb b/lib/lrucache.rb
index 735873c..221a63a 100644
--- a/lib/lrucache.rb
+++ b/lib/lrucache.rb
@@ -13,7 +13,7 @@ def initialize(opts={})
     @ttl = Float(opts[:ttl] || 0)
     @soft_ttl = Float(opts[:soft_ttl] || 0)
     @retry_delay = Float(opts[:retry_delay] || 0)
-    raise "max_size must not be negative" if @max_size < 0
+    raise "max_size must be greater than 0" if @max_size < 1
     raise "ttl must not be negative" if @ttl < 0
     raise "soft_ttl must not be negative" if @soft_ttl < 0
     raise "retry_delay must not be negative" if @retry_delay < 0
diff --git a/spec/lrucache_spec.rb b/spec/lrucache_spec.rb
index 8a1e00e..0e8a2d9 100644
--- a/spec/lrucache_spec.rb
+++ b/spec/lrucache_spec.rb
@@ -10,8 +10,9 @@
     it "should raise an exception if :max_size parameter can't be converted to an integer" do
       expect { LRUCache.new(:max_size => "moocow") }.to raise_exception
     end
-    it "should raise an exception if :max_size parameter is converted to a negative integer" do
+    it "should raise an exception if :max_size parameter is converted to a non-positive integer" do
       expect { LRUCache.new(:max_size => -1) }.to raise_exception
+      expect { LRUCache.new(:max_size => 0) }.to raise_exception
     end
 
     it "should default :default to nil" do