diff --git a/src/ferrolang_vm/test_cli.py b/src/ferrolang_vm/test_cli.py
index 075a525..d82b2ee 100644
--- a/src/ferrolang_vm/test_cli.py
+++ b/src/ferrolang_vm/test_cli.py
@@ -62,7 +62,18 @@ def main() -> int:
         # shell is sitting in -- an editable install plus a git worktree is enough
         # to silently build and test the wrong tree.  Say which tree this is.
         print(f"ferro-test: building {ROOT}", file=sys.stderr)
-        test_file = os.fspath(ROOT / "tools" / "tests" / "test_milestones_dosboxx.py")
+        tests = ROOT / "tools" / "tests"
+        # The host gates run first and take under a second. A missing declaration
+        # or an 8.3-illegal name would otherwise be found only after a DOSBox-X
+        # boot and a full compiler build, and the DOS-side message for either is
+        # unhelpful. They do not replace the DOS run; they precede it.
+        gates = [os.fspath(tests / name) for name in
+                 ("test_host_syntax.py", "test_dos_names.py")]
+        if pytest.main([*gates, "-q", "--no-header"]) != 0:
+            print("ferro-test: host gates failed; not starting DOSBox-X",
+                  file=sys.stderr)
+            return 1
+        test_file = os.fspath(tests / "test_milestones_dosboxx.py")
         pytest_args = [test_file, "--tb=short", "-v" if args.verbose else "-q"]
         if args.select:
             pytest_args.extend(["-k", args.select])
diff --git a/tools/tests/test_host_syntax.py b/tools/tests/test_host_syntax.py
new file mode 100644
index 0000000..56408e5
--- /dev/null
+++ b/tools/tests/test_host_syntax.py
@@ -0,0 +1,105 @@
+"""Compile the compiler's own sources on the host, as a syntax gate.
+
+This is not verification. AGENTS.md is explicit that a host compiler's result
+does not count, and it still does not: the DOS build and the milestone suite
+decide whether anything works. What this buys is the turnaround. A missing
+declaration or a signature that disagrees with its definition used to surface
+only after a DOSBox-X boot and a full compiler build; here it surfaces in about
+a second, with the line number.
+
+It uses the same Open Watcom the project targets, just the Windows-hosted build,
+and the same strictness as ``fec/build-dos.bat`` (``-za -wx -wcd=202``). The
+target differs -- wcc386 is 32-bit where the DOS build is 16-bit large model --
+so this catches syntax, types and declarations, not code generation or memory
+model problems.
+
+Skipped when Watcom is not installed, so the suite still runs anywhere.
+"""
+from __future__ import annotations
+
+import os
+import re
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+from ferrolang_vm.paths import ROOT
+
+SRC = ROOT / "fec" / "src"
+# Mirrors the compile order in fec/build-dos.bat.
+SOURCES = ("arena", "diag", "lexer", "ast", "parser", "types", "m7", "own",
+           "check", "lower", "emit_c", "driver")
+
+
+def _watcom() -> Path | None:
+    root = os.environ.get("WATCOM")
+    candidates = [Path(root)] if root else []
+    candidates.append(Path("C:/WATCOM19"))
+    for base in candidates:
+        if (base / "binnt" / "wcc386.exe").is_file():
+            return base
+    return None
+
+
+@pytest.fixture(scope="session")
+def watcom() -> Path:
+    base = _watcom()
+    if base is None:
+        pytest.skip("Open Watcom is not installed on the host; set WATCOM to enable")
+    return base
+
+
+@pytest.fixture(scope="session")
+def objdir(tmp_path_factory: pytest.TempPathFactory) -> Path:
+    return tmp_path_factory.mktemp("wcc")
+
+
+@pytest.mark.parametrize("name", SOURCES)
+def test_source_compiles_clean(name: str, watcom: Path, objdir: Path) -> None:
+    source = SRC / f"{name}.c"
+    if not source.is_file():
+        pytest.fail(f"{source} is missing but build-dos.bat compiles it")
+    env = dict(os.environ)
+    env["WATCOM"] = os.fspath(watcom)
+    env["INCLUDE"] = os.fspath(watcom / "h")
+    completed = subprocess.run(
+        [os.fspath(watcom / "binnt" / "wcc386.exe"), "-q", "-za", "-wx",
+         "-wcd=202", "-zq", f"-i={SRC}", os.fspath(source)],
+        cwd=objdir, capture_output=True, text=True, env=env, timeout=120,
+    )
+    output = (completed.stdout + completed.stderr).strip()
+    # -wx keeps warnings meaningful, so treat any diagnostic as a failure: the
+    # DOS build runs the same flags and stops on them.
+    assert completed.returncode == 0 and not output, (
+        f"{name}.c does not compile clean\n{output}"
+    )
+
+
+def test_build_scripts_agree_on_sources() -> None:
+    """The two build files and this test must name the same translation units.
+
+    They drifted apart while the M7 wrapper existed, which is how a source could
+    stop being compiled without anyone noticing.
+    """
+    batch = (ROOT / "fec" / "build-dos.bat").read_text(encoding="utf-8", errors="replace")
+    makefile = (ROOT / "fec" / "Makefile").read_text(encoding="utf-8", errors="replace")
+    in_batch = set(re.findall(r"src\\(\w+)\.c", batch))
+    srcline = next(line for line in makefile.splitlines() if line.startswith("SRC ="))
+    in_make = set(re.findall(r"src/(\w+)\.c", srcline))
+    assert in_batch == set(SOURCES), f"build-dos.bat compiles {sorted(in_batch)}"
+    assert in_make == set(SOURCES), f"Makefile compiles {sorted(in_make)}"
+
+
+def test_no_source_is_orphaned() -> None:
+    """Every .c under fec/src must be compiled by something.
+
+    check_m7.c and emitcm7.c hid check.c and emit_c.c from the build by
+    including them textually; nothing flagged that they had stopped being
+    translation units of their own.
+    """
+    on_disk = {p.stem for p in SRC.glob("*.c")}
+    assert on_disk == set(SOURCES), (
+        f"fec/src has {sorted(on_disk - set(SOURCES))} that no build step compiles"
+    )