diff --git a/lib/chunky_png/canvas/png_decoding.rb b/lib/chunky_png/canvas/png_decoding.rb
index <HASH>..<HASH> 100644
--- a/lib/chunky_png/canvas/png_decoding.rb
+++ b/lib/chunky_png/canvas/png_decoding.rb
@@ -385,7 +385,7 @@ module ChunkyPNG
           else nil
         end
         
-        raise ChunkyPNG::NotSupported, "No decoder found for color mode #{color_mode} and #{depth}-bit depth!" unless respond_to?(decoder_method)
+        raise ChunkyPNG::NotSupported, "No decoder found for color mode #{color_mode} and #{depth}-bit depth!" unless respond_to?(decoder_method, true)
         decoder_method
       end
 
diff --git a/lib/chunky_png/canvas/png_encoding.rb b/lib/chunky_png/canvas/png_encoding.rb
index <HASH>..<HASH> 100644
--- a/lib/chunky_png/canvas/png_encoding.rb
+++ b/lib/chunky_png/canvas/png_encoding.rb
@@ -367,7 +367,7 @@ module ChunkyPNG
           else nil
         end
         
-        raise ChunkyPNG::NotSupported, "No encoder found for color mode #{color_mode} and #{depth}-bit depth!" unless respond_to?(encoder_method)
+        raise ChunkyPNG::NotSupported, "No encoder found for color mode #{color_mode} and #{depth}-bit depth!" unless respond_to?(encoder_method, true)
         encoder_method
       end
Fix for ruby-head returning false to respond_to? for protected methods, unless a second argument is given.