diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9a5ee72c..d5705e2b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,7 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- n/a
+### Changed
+- Patterns to `Matcher.regex` are now more strictly typechecked when the matcher is created.
 
 ## [2.3.0] - 2019-09-25
 
diff --git a/pubtools/pulplib/_impl/criteria.py b/pubtools/pulplib/_impl/criteria.py
index 5739c4a2..bf7b0e07 100644
--- a/pubtools/pulplib/_impl/criteria.py
+++ b/pubtools/pulplib/_impl/criteria.py
@@ -256,6 +256,13 @@ class RegexMatcher(Matcher):
 
     @_pattern.validator
     def _check_pattern(self, _, pattern):
+        # It must be a string.
+        # Need an explicit check here because re.compile also succeeds
+        # on already-compiled regex objects.
+        if not isinstance(pattern, six.string_types):
+            raise TypeError("Regex matcher expected string, got: %s" % repr(pattern))
+
+        # Verify that the given value can really be compiled as a regex.
         re.compile(pattern)
 
     # Note: regex matcher does not implement _map since regex is defined only
diff --git a/tests/criteria/test_matcher.py b/tests/criteria/test_matcher.py
index 3cf2a985..1206cd1e 100644
--- a/tests/criteria/test_matcher.py
+++ b/tests/criteria/test_matcher.py
@@ -10,3 +10,10 @@ def test_matcher_regex_invalid():
 
     with pytest.raises(re.error):
         Matcher.regex("foo [bar")
+
+
+def test_matcher_regex_compiled():
+    """Matcher.regex raises if passed value is a compiled regex."""
+
+    with pytest.raises(TypeError):
+        Matcher.regex(re.compile("foobar"))