diff --git a/lib/paperclip/io_adapters/stringio_adapter.rb b/lib/paperclip/io_adapters/stringio_adapter.rb
index bd5f7d6d1..4084f783b 100644
--- a/lib/paperclip/io_adapters/stringio_adapter.rb
+++ b/lib/paperclip/io_adapters/stringio_adapter.rb
@@ -24,7 +24,10 @@ def size
     end
 
     def fingerprint
-      Digest::MD5.hexdigest(read)
+      rewind # start reading from the beginning
+      finger = Digest::MD5.hexdigest(read)
+      rewind
+      finger
     end
 
     def read(length = nil, buffer = nil)