diff --git a/lib/sprockets/utils.rb b/lib/sprockets/utils.rb
index 5e281c4f3..1233b78f7 100644
--- a/lib/sprockets/utils.rb
+++ b/lib/sprockets/utils.rb
@@ -98,7 +98,7 @@ def string_end_with_semicolon?(str)
     #
     # Returns buf String.
     def concat_javascript_sources(buf, source)
-      return buf if source.bytesize < 0
+      return buf if source.bytesize <= 0
 
       buf << source
       # If the source contains non-ASCII characters, indexing on it becomes O(N).