diff --git a/lib/postgres/postgres-pr/message.rb b/lib/postgres/postgres-pr/message.rb
index 643b688cdd..cb45a6724c 100644
--- a/lib/postgres/postgres-pr/message.rb
+++ b/lib/postgres/postgres-pr/message.rb
@@ -44,7 +44,7 @@ class Message
 
   def self.read(stream, startup=false)
     type = stream.read_exactly_n_bytes(1) unless startup
-    length = stream.read_exactly_n_bytes(4).unpack('N').first  # FIXME: length should be signed, not unsigned
+    length = stream.read_exactly_n_bytes(4).to_s.unpack('N').first  # FIXME: length should be signed, not unsigned
 
     raise ParseError unless length >= 4