diff --git a/bin/tests/system/.gitignore b/bin/tests/system/.gitignore
index c0f44047ac..a59bb20737 100644
--- a/bin/tests/system/.gitignore
+++ b/bin/tests/system/.gitignore
@@ -25,10 +25,8 @@ named.run
 !/isctest/vars/.build_vars/*.in
 !/isctest/vars/.build_vars/meson.build
 
-# Ignore file names with underscore in their name except python or shell files.
+# Ignore file names with a hyphen in their name except C files.
 # This is done to ignore the temporary directories and symlinks created by the
 # pytest runner, which contain underscore in their file names.
-/*_*
-!/*_*.py
-!/*_*.sh
-!/_common
+/*-*
+!/*-*.c
diff --git a/bin/tests/system/README.md b/bin/tests/system/README.md
index dc5f782779..96048c15a5 100644
--- a/bin/tests/system/README.md
+++ b/bin/tests/system/README.md
@@ -123,15 +123,12 @@ Each test module is executed inside a unique temporary directory which contains
 all the artifacts from the test run. If the tests succeed, they are deleted by
 default. To override this behaviour, pass `--noclean` to pytest.
 
-The directory name starts with the system test name, followed by `_tmp_XXXXXX`,
-i.e. `dns64_tmp_r07vei9s` for `dns64` test run. Since this name changes each
+The directory name starts with the system test name, followed by `-tmp-XXXXXX`,
+i.e. `dns64-tmp-r07vei9s` for `dns64` test run. Since this name changes each
 run, a convenience symlink that has a stable name is also created. It points to
-the latest test artifacts directory and has a form of `dns64_sh_dns64`
+the latest test artifacts directory and has a form of `dns64-sh_dns64`
 (depending on the particular test module).
 
-To clean up the temporary directories and symlinks, run `make clean-local` in
-the system test directory.
-
 The following test artifacts are typically available:
 
 - pytest.log.txt: main log file with test output
diff --git a/bin/tests/system/conftest.py b/bin/tests/system/conftest.py
index 4e7a1d7b1a..74af6c1b5e 100644
--- a/bin/tests/system/conftest.py
+++ b/bin/tests/system/conftest.py
@@ -54,7 +54,7 @@ PRIORITY_TESTS = [
 ]
 PRIORITY_TESTS_RE = Re("|".join(PRIORITY_TESTS))
 SYSTEM_TEST_NAME_RE = Re(f"{SYSTEM_TEST_DIR_GIT_PATH}" + r"/([^/]+)")
-SYMLINK_REPLACEMENT_RE = Re(r"/tests(_.*)\.py")
+SYMLINK_REPLACEMENT_RE = Re(r"/tests_(.*)\.py")
 
 # ----------------------- Global requirements ----------------------------
 
@@ -84,14 +84,14 @@ def pytest_ignore_collect(collection_path):
     # ignore these during test collection phase. Otherwise, test artifacts
     # from previous runs could mess with the runner. Also ignore the
     # convenience symlinks to those test directories. In both of those
-    # cases, the system test name (directory) contains an underscore, which
+    # cases, the system test name (directory) contains a hyphen, which
     # is otherwise and invalid character for a system test name.
     match = SYSTEM_TEST_NAME_RE.search(str(collection_path))
     if match is None:
         isctest.log.warning("unexpected test path: %s (ignored)", collection_path)
         return True
     system_test_name = match.groups()[0]
-    return "_" in system_test_name
+    return "-" in system_test_name
 
 
 def pytest_collection_modifyitems(items):
@@ -385,14 +385,14 @@ def system_test_dir(request, system_test_name, expected_artifacts):
     # Create a temporary directory with a copy of the original system test dir contents
     system_test_root = Path(os.environ["srcdir"]).resolve()
     testdir = Path(
-        tempfile.mkdtemp(prefix=f"{system_test_name}_tmp_", dir=system_test_root)
+        tempfile.mkdtemp(prefix=f"{system_test_name}-tmp-", dir=system_test_root)
     )
     shutil.rmtree(testdir)
     shutil.copytree(system_test_root / system_test_name, testdir)
     isctest.vars.dirs.set_system_test_name(testdir.name)
 
     # Create a convenience symlink with a stable and predictable name
-    module_name = SYMLINK_REPLACEMENT_RE.sub(r"\1", str(request.node.path))
+    module_name = SYMLINK_REPLACEMENT_RE.sub(r"-\1", str(request.node.path))
     symlink_dst = system_test_root / module_name
     symlink_dst.unlink(missing_ok=True)
     symlink_dst.symlink_to(os.path.relpath(testdir, start=system_test_root))
diff --git a/dangerfile.py b/dangerfile.py
index e2ba7d48fd..33f2fbe4fe 100644
--- a/dangerfile.py
+++ b/dangerfile.py
@@ -483,10 +483,10 @@ for testname in testnames:
         or testname == "isctest"
     ):
         continue
-    if "_" in testname:
+    if "-" in testname:
         fail(
-            f"System test directory `{testname}` may not contain an underscore, "
-            "use hyphen instead."
+            f"System test directory `{testname}` may not contain a hyphen, "
+            "use underscore instead."
         )
     if not glob.glob(f"{dirpath}/**/tests_*.py", recursive=True):
         fail(