diff --git a/irctest/irc_utils/message_parser.py b/irctest/irc_utils/message_parser.py
index f24a549..ba0ec45 100644
--- a/irctest/irc_utils/message_parser.py
+++ b/irctest/irc_utils/message_parser.py
@@ -15,7 +15,7 @@ TAG_ESCAPE = [
 unescape_tag_value = MultipleReplacer(dict(map(lambda x: (x[1], x[0]), TAG_ESCAPE)))
 
 # TODO: validate host
-tag_key_validator = re.compile(r"\+?(\S+/)?[a-zA-Z0-9-]+")
+tag_key_validator = re.compile(r"^\+?(\S+/)?[a-zA-Z0-9-]+$")
 
 
 def parse_tags(s: str) -> Dict[str, Optional[str]]:
diff --git a/irctest/patma.py b/irctest/patma.py
index c121414..a9c3db9 100644
--- a/irctest/patma.py
+++ b/irctest/patma.py
@@ -106,15 +106,15 @@ def match_string(got: Optional[str], expected: Union[str, Operator, None]) -> bo
     elif isinstance(expected, _AnyStr) and got is not None:
         return True
     elif isinstance(expected, StrRe):
-        if got is None or not re.match(expected.regexp, got):
+        if got is None or not re.match(expected.regexp + "$", got):
             return False
     elif isinstance(expected, OptStrRe):
         if got is None:
             return True
-        if not re.match(expected.regexp, got):
+        if not re.match(expected.regexp + "$", got):
             return False
     elif isinstance(expected, NotStrRe):
-        if got is None or re.match(expected.regexp, got):
+        if got is None or re.match(expected.regexp + "$", got):
             return False
     elif isinstance(expected, InsensitiveStr):
         if got is None or got.lower() != expected.string.lower():
diff --git a/irctest/server_tests/isupport.py b/irctest/server_tests/isupport.py
index 1848098..8dd1c51 100644
--- a/irctest/server_tests/isupport.py
+++ b/irctest/server_tests/isupport.py
@@ -56,7 +56,8 @@ class IsupportTestCase(cases.BaseServerTestCase):
             return
 
         m = re.match(
-            r"\((?P<modes>[a-zA-Z]+)\)(?P<prefixes>\S+)", self.server_support["PREFIX"]
+            r"^\((?P<modes>[a-zA-Z]+)\)(?P<prefixes>\S+)$",
+            self.server_support["PREFIX"],
         )
         self.assertTrue(
             m,
@@ -117,5 +118,5 @@ class IsupportTestCase(cases.BaseServerTestCase):
         parts = self.server_support["TARGMAX"].split(",")
         for part in parts:
             self.assertTrue(
-                re.match("[A-Z]+:[0-9]*", part), "Invalid TARGMAX key:value: %r", part
+                re.match("^[A-Z]+:[0-9]*$", part), "Invalid TARGMAX key:value: %r", part
             )