diff --git a/lib/postgres/postgres-pr/message.rb b/lib/postgres/postgres-pr/message.rb
index 8041c7ced9..b2844a05c7 100644
--- a/lib/postgres/postgres-pr/message.rb
+++ b/lib/postgres/postgres-pr/message.rb
@@ -46,7 +46,7 @@ class Message
     type = stream.read_exactly_n_bytes(1) unless startup
     length = stream.read_exactly_n_bytes(4).to_s.unpack('N').first  # FIXME: length should be signed, not unsigned
 
-    raise ParseError unless (!length.nil? && length >= 4)
+    raise ParseError if (!length.nil? || length >= 4)
 
     # If we didn't read any bytes and startup was not set, then type will be nil, so don't continue.
     unless startup