diff --git a/validators/url.py b/validators/url.py
index fe2cbf53..4db869b9 100644
--- a/validators/url.py
+++ b/validators/url.py
@@ -69,7 +69,7 @@
     r"(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])"
     r")\]|"
     # host name
-    r"(?:(?:(?:xn--)|[a-z\u00a1-\uffff\U00010000-\U0010ffff0-9]-?)*"
+    r"(?:(?:(?:xn--)|[a-z\u00a1-\uffff\U00010000-\U0010ffff0-9_]-?)*"
     r"[a-z\u00a1-\uffff\U00010000-\U0010ffff0-9]+)"
     # domain name
     r"(?:\.(?:(?:xn--)|[a-z\u00a1-\uffff\U00010000-\U0010ffff0-9]-?)*"