diff --git a/tests/conformance/conftest.py b/tests/conformance/conftest.py
index 43219b2..80bf0ea 100644
--- a/tests/conformance/conftest.py
+++ b/tests/conformance/conftest.py
@@ -13,6 +13,24 @@
 ROOT = Path(__file__).resolve().parents[2]
 
 
+# A compiler launcher in front of the toolchain runs as part of the build and
+# lands in the recording, so a diff test would describe whichever launcher the
+# machine happens to have installed. Tests that want one put it on PATH
+# themselves.
+LAUNCHERS = frozenset({"ccache", "distcc", "icecc", "sccache"})
+
+
+@pytest.fixture
+def plain_environment() -> dict[str, str]:
+    """The environment with any compiler launcher taken off `PATH`."""
+    directories = [
+        directory
+        for directory in os.environ.get("PATH", "").split(os.pathsep)
+        if not LAUNCHERS & set(Path(directory).parts)
+    ]
+    return dict(os.environ, LC_ALL="C", PATH=os.pathsep.join(directories))
+
+
 def pytest_addoption(parser: pytest.Parser) -> None:
     parser.addoption(
         "--update-expectations",
diff --git a/tests/conformance/test_build_systems.py b/tests/conformance/test_build_systems.py
index 2ead5e9..7fe5d12 100644
--- a/tests/conformance/test_build_systems.py
+++ b/tests/conformance/test_build_systems.py
@@ -200,7 +200,9 @@ def tool_of(pid: int) -> str:
 
 
 @pytest.mark.parametrize("case", sorted(CASES))
-def test_build_system(case, buildprof: Path, tmp_path: Path, request):
+def test_build_system(
+    case, buildprof: Path, tmp_path: Path, request, plain_environment: dict
+):
     for tool in REQUIRED_TOOLS[case]:
         if shutil.which(tool) is None:
             message = f"{tool} is not installed in this environment"
@@ -214,14 +216,13 @@ def test_build_system(case, buildprof: Path, tmp_path: Path, request):
     command = build(project)
 
     trace = tmp_path / f"{case}.pftrace"
-    env = dict(os.environ, LC_ALL="C")
     result = subprocess.run(
         [str(buildprof), "-o", str(trace), "--", *command],
         cwd=project,
         text=True,
         capture_output=True,
         timeout=300,
-        env=env,
+        env=plain_environment,
     )
     assert result.returncode == 0, f"{case} build failed:\n{result.stdout}{result.stderr}"
     assert trace.is_file(), f"{case} produced no trace"
@@ -241,7 +242,7 @@ def test_build_system(case, buildprof: Path, tmp_path: Path, request):
     )
 
 
-def test_npm_build(buildprof: Path, tmp_path: Path):
+def test_npm_build(buildprof: Path, tmp_path: Path, plain_environment: dict):
     for tool in ("npm", "node"):
         if shutil.which(tool) is None:
             message = f"{tool} is not installed in this environment"
@@ -254,7 +255,7 @@ def test_npm_build(buildprof: Path, tmp_path: Path):
     result = subprocess.run(
         [str(buildprof), "--no-open", "-o", str(trace), "--", *command],
         cwd=tmp_path,
-        env=dict(os.environ, LC_ALL="C", npm_config_cache=str(tmp_path / ".npm")),
+        env=dict(plain_environment, npm_config_cache=str(tmp_path / ".npm")),
         text=True,
         capture_output=True,
         timeout=60,