diff --git a/app/logical/apng_inspector.rb b/app/logical/apng_inspector.rb
index 5fa97b302..4162e043a 100644
--- a/app/logical/apng_inspector.rb
+++ b/app/logical/apng_inspector.rb
@@ -40,7 +40,7 @@ class ApngInspector
       chunkheader = +""
       while file.read(8, chunkheader)
         #ensure that first 8 bytes from chunk were read properly
-        if chunkheader == nil || chunkheader.length < 8
+        if chunkheader == nil || chunkheader.bytesize < 8
           return false
         end