diff --git a/conformance/scripts/check_conformance_policy.py b/conformance/scripts/check_conformance_policy.py
index 54d3bd6..f856fb0 100644
--- a/conformance/scripts/check_conformance_policy.py
+++ b/conformance/scripts/check_conformance_policy.py
@@ -41,14 +41,15 @@ def split_patterns(value: str) -> list[str]:
 
 def path_matches(path: str, pattern: str) -> bool:
     normalized = path.strip("/")
+    is_dir_pattern = pattern.endswith("/")
     normalized_pattern = pattern.strip("/")
     if not normalized_pattern:
         return False
     if normalized_pattern.endswith("/**"):
         prefix = normalized_pattern[:-3].rstrip("/")
         return normalized == prefix or normalized.startswith(prefix + "/")
-    if normalized_pattern.endswith("/"):
-        return normalized.startswith(normalized_pattern)
+    if is_dir_pattern:
+        return normalized.startswith(normalized_pattern + "/")
     return fnmatchcase(normalized, normalized_pattern)
 
 
diff --git a/conformance/scripts/select_ci_adapters.py b/conformance/scripts/select_ci_adapters.py
index af80733..57c500e 100755
--- a/conformance/scripts/select_ci_adapters.py
+++ b/conformance/scripts/select_ci_adapters.py
@@ -52,12 +52,15 @@
 
 def path_matches(path: str, pattern: str) -> bool:
     normalized = path.strip("/")
+    is_dir_pattern = pattern.endswith("/")
     normalized_pattern = pattern.strip("/")
+    if not normalized_pattern:
+        return False
     if normalized_pattern.endswith("/**"):
         prefix = normalized_pattern[:-3].rstrip("/")
         return normalized == prefix or normalized.startswith(prefix + "/")
-    if normalized_pattern.endswith("/"):
-        return normalized.startswith(normalized_pattern)
+    if is_dir_pattern:
+        return normalized.startswith(normalized_pattern + "/")
     return fnmatchcase(normalized, normalized_pattern)
 
 
diff --git a/conformance/scripts/test_check_conformance_policy.py b/conformance/scripts/test_check_conformance_policy.py
index 2f73f16..3abad5b 100644
--- a/conformance/scripts/test_check_conformance_policy.py
+++ b/conformance/scripts/test_check_conformance_policy.py
@@ -3,6 +3,7 @@
 
 from __future__ import annotations
 
+import importlib
 import json
 import os
 import subprocess
@@ -14,6 +15,54 @@
 
 SCRIPT = Path(__file__).with_name("check_conformance_policy.py")
 
+# Modules that each carry a copy of path_matches and must stay in sync.
+PATH_MATCH_MODULES = [
+    "check_conformance_policy",
+    "validate_conformance_pr",
+    "select_ci_adapters",
+]
+
+
+class PathMatchesTest(unittest.TestCase):
+    def each_path_matches(self):
+        sys.path.insert(0, str(SCRIPT.parent))
+        try:
+            for module_name in PATH_MATCH_MODULES:
+                module = importlib.import_module(module_name)
+                yield module_name, module.path_matches
+        finally:
+            sys.path.remove(str(SCRIPT.parent))
+
+    def test_directory_pattern_matches_files_under_directory(self) -> None:
+        for module_name, path_matches in self.each_path_matches():
+            with self.subTest(module=module_name):
+                self.assertTrue(path_matches("src/proto/wire.go", "src/proto/"))
+                self.assertTrue(path_matches("src/proto/nested/deep.rs", "src/proto/"))
+                self.assertTrue(path_matches("/src/proto/wire.go", "src/proto/"))
+
+    def test_directory_pattern_does_not_overmatch(self) -> None:
+        for module_name, path_matches in self.each_path_matches():
+            with self.subTest(module=module_name):
+                self.assertFalse(path_matches("src/protocol/wire.go", "src/proto/"))
+                self.assertFalse(path_matches("src/proto", "src/proto/"))
+                self.assertFalse(path_matches("other/src/proto/wire.go", "src/proto/"))
+
+    def test_recursive_glob_pattern_still_matches(self) -> None:
+        for module_name, path_matches in self.each_path_matches():
+            with self.subTest(module=module_name):
+                self.assertTrue(path_matches("conformance/vectors/receipt.json", "conformance/vectors/**"))
+                self.assertTrue(path_matches("conformance/vectors", "conformance/vectors/**"))
+                self.assertFalse(path_matches("conformance/schemas/x.json", "conformance/vectors/**"))
+
+    def test_exact_and_glob_patterns_still_match(self) -> None:
+        for module_name, path_matches in self.each_path_matches():
+            with self.subTest(module=module_name):
+                self.assertTrue(path_matches("conformance/operations.json", "conformance/operations.json"))
+                self.assertTrue(path_matches("pkg/parse.go", "pkg/*.go"))
+                self.assertFalse(path_matches("pkg/readme.md", "pkg/*.go"))
+                self.assertFalse(path_matches("pkg/parse.go", ""))
+                self.assertFalse(path_matches("pkg/parse.go", "/"))
+
 
 class CheckConformancePolicyTest(unittest.TestCase):
     def run_policy(
diff --git a/conformance/scripts/validate_conformance_pr.py b/conformance/scripts/validate_conformance_pr.py
index 220d10c..49be48a 100755
--- a/conformance/scripts/validate_conformance_pr.py
+++ b/conformance/scripts/validate_conformance_pr.py
@@ -19,12 +19,15 @@ def split_patterns(value: str) -> list[str]:
 
 def path_matches(path: str, pattern: str) -> bool:
     normalized = path.strip("/")
+    is_dir_pattern = pattern.endswith("/")
     normalized_pattern = pattern.strip("/")
+    if not normalized_pattern:
+        return False
     if normalized_pattern.endswith("/**"):
         prefix = normalized_pattern[:-3].rstrip("/")
         return normalized == prefix or normalized.startswith(prefix + "/")
-    if normalized_pattern.endswith("/"):
-        return normalized.startswith(normalized_pattern)
+    if is_dir_pattern:
+        return normalized.startswith(normalized_pattern + "/")
     return fnmatchcase(normalized, normalized_pattern)