diff --git a/tests/rules/test_line_length.py b/tests/rules/test_line_length.py
index d63afb3..fc3f0e8 100644
--- a/tests/rules/test_line_length.py
+++ b/tests/rules/test_line_length.py
@@ -116,6 +116,16 @@ class LineLengthTestCase(RuleTestCase):
                    'long_line: http://localhost/very/very/long/url\n'
                    '...\n', conf, problem=(2, 21))
 
+        conf = 'line-length: {max: 20, allow-non-breakable-words: true}'
+        self.check('---\n'
+                   '# http://www.verylongurlurlurlurlurlurlurlurl.com\n'
+                   'key:\n'
+                   '  value:\n', conf)
+        self.check('---\n'
+                   '## http://www.verylongurlurlurlurlurlurlurlurl.com\n'
+                   'key:\n'
+                   '  value:\n', conf)
+
         conf = ('line-length: {max: 20, allow-non-breakable-words: true}\n'
                 'trailing-spaces: disable')
         self.check('---\n'
diff --git a/yamllint/rules/line_length.py b/yamllint/rules/line_length.py
index 0431240..0289747 100644
--- a/yamllint/rules/line_length.py
+++ b/yamllint/rules/line_length.py
@@ -140,7 +140,11 @@ def check(conf, line):
                 start += 1
 
             if start != line.end:
-                if line.buffer[start] in ('#', '-'):
+                if line.buffer[start] in ('#'):
+                    idx = line.buffer.find(' ', start, line.end)
+                    if idx != -1:
+                        start = idx + 1
+                elif line.buffer[start] in ('-'):
                     start += 2
 
                 if line.buffer.find(' ', start, line.end) == -1: