diff --git a/Gemfile.lock b/Gemfile.lock
index cf35e06b..f1945b11 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    compass (0.11.beta.3.a4d4319)
+    compass (0.11.beta.3.acf9c66)
       chunky_png (~> 1.1.0)
       sass (>= 3.1.0.alpha.249)
 
diff --git a/lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb b/lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb
index f9a43e8a..3990cd45 100644
--- a/lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb
+++ b/lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb
@@ -20,7 +20,7 @@ module Compass
             else
               x = image.left - (image.left / image.width).ceil * image.width
               while x < width do
-                output_png.replace input_png, x, image.top
+                output_png.replace! input_png, x, image.top
                 x += image.width
               end
             end
diff --git a/spec/sprites_spec.rb b/spec/sprites_spec.rb
index 94349518..700610eb 100644
--- a/spec/sprites_spec.rb
+++ b/spec/sprites_spec.rb
@@ -88,7 +88,7 @@ describe Compass::Sprites do
       }
     CSS
     image_size('squares-*.png').should == [20, 30]
-    image_md5('squares-*.png').should == 'fcc93d7b279c2ad6898fbca49cbd01e1'
+    image_md5('squares-*.png').should == 'd1aff60ac2f10dcc9859309d36f7e9a0'
   end
 
   it "should generate sprite classes with dimensions" do
@@ -311,7 +311,7 @@ describe Compass::Sprites do
       }
     CSS
     image_size('squares-*.png').should == [20, 30]
-    image_md5('squares-*.png').should == '652b67f5e9092520d6f26caae7e18012'
+    image_md5('squares-*.png').should == 'd1aff60ac2f10dcc9859309d36f7e9a0'
   end
 
   it "should use position adjustments in mixins" do
@@ -349,7 +349,7 @@ describe Compass::Sprites do
       }
     CSS
     image_size('squares-*.png').should == [20, 30]
-    image_md5('squares-*.png').should == '652b67f5e9092520d6f26caae7e18012'
+    image_md5('squares-*.png').should == 'd1aff60ac2f10dcc9859309d36f7e9a0'
   end
 
   it "should repeat the image" do
@@ -396,7 +396,7 @@ describe Compass::Sprites do
       }
     CSS
     image_size('squares-*.png').should == [30, 30]
-    image_md5('squares-*.png').should == '2fb19ef9c83018c93c6f147af3a56cb2'
+    image_md5('squares-*.png').should == '33b385d541ce887441606e75467fd7ef'
   end
 
   it "should provide a nice errors for lemonade's old users" do