diff --git a/django/core/validators.py b/django/core/validators.py
index 15b16bcd2f..8c43644ed6 100644
--- a/django/core/validators.py
+++ b/django/core/validators.py
@@ -83,9 +83,10 @@ class URLValidator(RegexValidator):
     ipv6_re = r'\[[0-9a-f:\.]+\]'  # (simple regex, validated later)
 
     # Host patterns
-    hostname_re = r'[a-z' + ul + r'0-9](?:[a-z' + ul + r'0-9-]*[a-z' + ul + r'0-9])?'
-    domain_re = r'(?:\.(?!-)[a-z' + ul + r'0-9-]+(?<!-))*'
-    tld_re = r'\.(?:[a-z' + ul + r']{2,}|xn--[a-z0-9]+)\.?'
+    hostname_re = r'[a-z' + ul + r'0-9](?:[a-z' + ul + r'0-9-]{0,61}[a-z' + ul + r'0-9])?'
+    # Max length for domain name labels is 63 characters per RFC 1034 sec. 3.1
+    domain_re = r'(?:\.(?!-)[a-z' + ul + r'0-9-]{1,63}(?<!-))*'
+    tld_re = r'\.(?:[a-z' + ul + r']{2,63}|xn--[a-z0-9]{1,59})\.?'
     host_re = '(' + hostname_re + domain_re + tld_re + '|localhost)'
 
     regex = _lazy_re_compile(
@@ -136,6 +137,13 @@ class URLValidator(RegexValidator):
                     raise ValidationError(self.message, code=self.code)
             url = value
 
+        # The maximum length of a full host name is 253 characters per RFC 1034
+        # section 3.1. It's defined to be 255 bytes or less, but this includes
+        # one byte for the length of the name and one byte for the trailing dot
+        # that's used to indicate absolute names in DNS.
+        if len(urlsplit(value).netloc) > 253:
+            raise ValidationError(self.message, code=self.code)
+
 integer_validator = RegexValidator(
     _lazy_re_compile('^-?\d+\Z'),
     message=_('Enter a valid integer.'),
diff --git a/docs/releases/1.10.txt b/docs/releases/1.10.txt
index 932d53b029..bee3b1d41f 100644
--- a/docs/releases/1.10.txt
+++ b/docs/releases/1.10.txt
@@ -258,7 +258,9 @@ URLs
 Validators
 ^^^^^^^^^^
 
-* ...
+* :class:`~django.core.validators.URLValidator` now limits the length of
+  domain name labels to 63 characters and the total length of domain
+  names to 253 characters per :rfc:`1034`.
 
 Backwards incompatible changes in 1.10
 ======================================
diff --git a/tests/validators/invalid_urls.txt b/tests/validators/invalid_urls.txt
index 12a1226359..f7dc1e238a 100644
--- a/tests/validators/invalid_urls.txt
+++ b/tests/validators/invalid_urls.txt
@@ -50,3 +50,7 @@ http://[::1:2::3]:8080/
 http://[]
 http://[]:8080
 http://example..com/
+http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.example.com
+http://example.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.com
+http://example.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaa
diff --git a/tests/validators/valid_urls.txt b/tests/validators/valid_urls.txt
index ad30811177..0dc4d61bea 100644
--- a/tests/validators/valid_urls.txt
+++ b/tests/validators/valid_urls.txt
@@ -63,3 +63,7 @@ http://0.0.0.0/
 http://255.255.255.255
 http://224.0.0.0
 http://224.1.1.1
+http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.example.com
+http://example.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.com
+http://example.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+http://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaa