diff --git a/tools/optional-requires b/tools/optional-requires
index a17b1752..36c89ec0 100644
--- a/tools/optional-requires
+++ b/tools/optional-requires
@@ -1,4 +1,4 @@
-lxml      # OF-Config
+lxml!=3.7.0,>=2.3    # OF-Config
 ncclient  # OF-Config
 cryptography!=1.5.2  # Required by paramiko
 paramiko  # NETCONF, BGP speaker (SSH console)