diff --git a/pagure/pfmarkdown.py b/pagure/pfmarkdown.py
index 9fe6ddf..3d342a5 100644
--- a/pagure/pfmarkdown.py
+++ b/pagure/pfmarkdown.py
@@ -31,9 +31,16 @@ import pagure.lib
 from pagure.config import config as pagure_config
 
 
-MENTION_RE = r'@(\w+)'
+# the (?<!\w) (and variants) we use a lot in all these regexes is a
+# negative lookbehind assertion. It means 'match when the preceding
+# character is not in the \w class'. This stops us from starting a
+# match in the middle of a word (e.g. someone@something in the
+# MENTION_RE regex). Note that it is a zero-length match - it does
+# not capture or consume any of the string - and it does not appear
+# as a group for the match object.
+MENTION_RE = r'(?<!\w)@(\w+)'
 # Each line below correspond to a line of the regex:
-#  1) Ensure we catch the motif from the start
+#  1) Don't start matching in the middle of a word
 #  2) See if there is a `forks/` at the start
 #  3) See if we have a `user/`
 #  4) See if we have a `namespace/`
@@ -68,7 +75,7 @@ class MentionPattern(markdown.inlinepatterns.Pattern):
     def handleMatch(self, m):
         """ When the pattern matches, update the text. """
         name = markdown.util.AtomicString(m.group(2))
-        text = ' @%s' % name
+        text = '@%s' % name
         user = pagure.lib.search_user(flask.g.session, username=name)
         if not user:
             return text
diff --git a/tests/test_pagure_lib.py b/tests/test_pagure_lib.py
index 8d20c89..784b38f 100644
--- a/tests/test_pagure_lib.py
+++ b/tests/test_pagure_lib.py
@@ -4235,6 +4235,9 @@ class PagureLibtests(tests.Modeltests):
             "NoSuchDynamicUser'~~",
             '``~~foo bar~~``',
             '~~foo bar~~ and ~~another ~~',
+            'lets mention @pingou',
+            '@pingou at start of line',
+            'but not someone@pingou.com',
         ]
         expected = [
             # 'foo bar test#1 see?',
@@ -4319,6 +4322,12 @@ class PagureLibtests(tests.Modeltests):
             '<p><code>~~foo bar~~</code></p>',
             # '~~foo bar~~ and ~~another ~~',
             '<p><del>foo bar</del> and <del>another </del></p>',
+            # 'lets mention @pingou',
+            '<p>lets mention <a href="https://pagure.org/user/pingou">@pingou</a></p>',
+            # '@pingou at start of line',
+            '<p><a href="https://pagure.org/user/pingou">@pingou</a> at start of line</p>',
+            # 'but not someone@pingou.com',
+            '<p>but not someone@pingou.com</p>',
         ]
 
         with self.app.application.app_context():