diff --git a/kallithea/lib/helpers.py b/kallithea/lib/helpers.py
--- a/kallithea/lib/helpers.py
+++ b/kallithea/lib/helpers.py
@@ -1156,17 +1156,15 @@ def urlify_issues(newtext, repo_name):
 
             def issues_replace(match_obj,
                                issue_server_link=issue_server_link, issue_prefix=issue_prefix):
-                leadingspace = ' ' if match_obj.group().startswith(' ') else ''
                 issue_id = ''.join(match_obj.groups())
                 issue_url = issue_server_link.replace('{id}', issue_id)
                 issue_url = issue_url.replace('{repo}', repo_name)
                 issue_url = issue_url.replace('{repo_name}', repo_name.split(URL_SEP)[-1])
                 return (
-                    '%(leadingspace)s<a class="issue-tracker-link" href="%(url)s">'
+                    '<a class="issue-tracker-link" href="%(url)s">'
                     '%(issue-prefix)s%(id-repr)s'
                     '</a>'
                     ) % {
-                     'leadingspace': leadingspace,
                      'url': issue_url,
                      'id-repr': issue_id,
                      'issue-prefix': issue_prefix,
diff --git a/kallithea/lib/paster_commands/template.ini.mako b/kallithea/lib/paster_commands/template.ini.mako
--- a/kallithea/lib/paster_commands/template.ini.mako
+++ b/kallithea/lib/paster_commands/template.ini.mako
@@ -267,6 +267,9 @@ default_encoding = utf8
 <%text>## pattern to get the issues from commit messages</%text>
 <%text>## default one used here is #<numbers> with a regex passive group for `#`</%text>
 <%text>## {id} will be all groups matched from this pattern</%text>
+<%text>## To require mandatory whitespace before the issue pattern, use:</%text>
+<%text>## (?:^|(?<=\s)) before the actual pattern, and for mandatory whitespace</%text>
+<%text>## behind the issue pattern, use (?:$|(?=\s)) after the actual pattern</%text>
 
 issue_pat = #(\d+)
 
diff --git a/kallithea/tests/other/test_libs.py b/kallithea/tests/other/test_libs.py
--- a/kallithea/tests/other/test_libs.py
+++ b/kallithea/tests/other/test_libs.py
@@ -411,22 +411,34 @@ class TestLibs(TestController):
             'issue #123 and issue#456',
             """issue <a class="issue-tracker-link" href="http://foo/repo_name/issue/123">#123</a> and """
             """issue<a class="issue-tracker-link" href="http://foo/repo_name/issue/456">#456</a>"""),
+        # following test case shows the result of a backward incompatible change that was made: the
+        # space between 'issue' and '#123' is removed, because the space is part of the pattern.
         (r'(?:\s*#)(\d+)', 'http://foo/{repo}/issue/{id}', '#',
             'issue #123 and issue#456',
-            """issue <a class="issue-tracker-link" href="http://foo/repo_name/issue/123">#123</a> and """
+            """issue<a class="issue-tracker-link" href="http://foo/repo_name/issue/123">#123</a> and """
             """issue<a class="issue-tracker-link" href="http://foo/repo_name/issue/456">#456</a>"""),
+        # to require whitespace before the issue reference, one may be tempted to use \b...
         (r'\bPR(\d+)', 'http://foo/{repo}/issue/{id}', '#',
             'issue PR123 and issuePR456',
             """issue <a class="issue-tracker-link" href="http://foo/repo_name/issue/123">#123</a> and """
             """issuePR456"""),
-        # following test case shows that \b does not work well in combination with '#': the expectations
+        # ... but it turns out that \b does not work well in combination with '#': the expectations
         # are reversed from what is actually happening.
         (r'\b#(\d+)', 'http://foo/{repo}/issue/{id}', '#',
             'issue #123 and issue#456',
             """issue #123 and """
             """issue<a class="issue-tracker-link" href="http://foo/repo_name/issue/456">#456</a>"""),
-        (r'[ \t]#(\d+)', 'http://foo/{repo}/issue/{id}', '#',
-            'issue #123 and issue#456',
+        # ... so maybe try to be explicit? Unfortunately the whitespace before the issue
+        # reference is not retained, again, because it is part of the pattern.
+        (r'(?:^|\s)#(\d+)', 'http://foo/{repo}/issue/{id}', '#',
+            '#15 and issue #123 and issue#456',
+            """<a class="issue-tracker-link" href="http://foo/repo_name/issue/15">#15</a> and """
+            """issue<a class="issue-tracker-link" href="http://foo/repo_name/issue/123">#123</a> and """
+            """issue#456"""),
+        # ... instead, use lookbehind assertions.
+        (r'(?:^|(?<=\s))#(\d+)', 'http://foo/{repo}/issue/{id}', '#',
+            '#15 and issue #123 and issue#456',
+            """<a class="issue-tracker-link" href="http://foo/repo_name/issue/15">#15</a> and """
             """issue <a class="issue-tracker-link" href="http://foo/repo_name/issue/123">#123</a> and """
             """issue#456"""),
         (r'(?:pullrequest|pull request|PR|pr) ?#?(\d+)', 'http://foo/{repo}/issue/{id}', 'PR#',