diff --git a/lib/jekyll-webp/webpGenerator.rb b/lib/jekyll-webp/webpGenerator.rb
index 7548d6e..6af7c59 100644
--- a/lib/jekyll-webp/webpGenerator.rb
+++ b/lib/jekyll-webp/webpGenerator.rb
@@ -61,8 +61,14 @@ def generate(site)
           FileUtils::mkdir_p(imgdir_destination)
           Jekyll.logger.info "WebP:","Processing #{imgdir_source}"
 
+          # append a / if missing
+          imgdir_search_prefix = imgdir_source
+          if !imgdir_source.end_with?("/") then
+            imgdir_search_prefix = imgdir_source + "/"
+          end
+
           # handle only jpg, jpeg, png and gif
-          for imgfile in Dir[imgdir_source + "**/*.*"]
+          for imgfile in Dir[imgdir_search_prefix + "**/*.*"]
               imgfile_relative_path = File.dirname(imgfile.sub(imgdir_source, ""))
 
               # Skip empty stuff