diff --git a/stacklet/client/sinistral/commands/dump.py b/stacklet/client/sinistral/commands/dump.py
index 95a909d..1aed87f 100644
--- a/stacklet/client/sinistral/commands/dump.py
+++ b/stacklet/client/sinistral/commands/dump.py
@@ -2,15 +2,23 @@
 # SPDX-License-Identifier: Apache-2.0
 import sys
 
+from pathlib import Path
+
 import click
 
 from c7n_left.cli import dump as left_dump
+from c7n_left.core import get_provider
+from c7n_left.entry import initialize_iac
 
 
 class LeftWrapper(click.core.Command):
     def make_parser(self, ctx):
+        existing = {param.name for param in self.params}
         for param in left_dump.params:
-            self.params.append(param)
+            # make_parser runs on every invocation; the dump command is a
+            # module-level singleton, so skip params already appended.
+            if param.name not in existing:
+                self.params.append(param)
         return super().make_parser(ctx)
 
 
@@ -18,4 +26,11 @@ def make_parser(self, ctx):
 @click.pass_context
 def dump(ctx, *args, **kwargs):
     """Dump the IaC resource graph and input variables"""
+    # c7n-left registers its IaC providers in its own cli group callback,
+    # which is bypassed when invoking the dump subcommand directly.
+    initialize_iac()
+    if not ctx.params.get("directory"):
+        ctx.params["directory"] = "."
+    if get_provider(Path(ctx.params["directory"])) is None:
+        raise click.UsageError(f"No supported IaC files found in {ctx.params['directory']}")
     sys.exit(left_dump.invoke(ctx))
diff --git a/tests/test_dump.py b/tests/test_dump.py
new file mode 100644
index 0000000..08c063a
--- /dev/null
+++ b/tests/test_dump.py
@@ -0,0 +1,46 @@
+# Copyright Stacklet, Inc.
+# SPDX-License-Identifier: Apache-2.0
+import json
+import pathlib
+import subprocess
+import sys
+
+
+TERRAFORM_DIR = pathlib.Path(__file__).parent.resolve() / "terraform" / "good"
+
+
+def run_dump(*args, cwd=None):
+    # Run in a fresh interpreter: c7n-left registers its IaC providers via
+    # import side effects, so in-process tests could pass only because an
+    # earlier test happened to register them.
+    return subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            "from stacklet.client.sinistral.cli import cli; cli()",
+            "dump",
+            *args,
+        ],
+        check=False,
+        capture_output=True,
+        text=True,
+        cwd=cwd,
+    )
+
+
+def test_dump_directory():
+    result = run_dump("-d", str(TERRAFORM_DIR))
+    assert result.returncode == 0, result.stderr
+    assert "aws_sqs_queue" in json.loads(result.stdout)["graph"]
+
+
+def test_dump_defaults_to_current_directory():
+    result = run_dump(cwd=TERRAFORM_DIR)
+    assert result.returncode == 0, result.stderr
+    assert "aws_sqs_queue" in json.loads(result.stdout)["graph"]
+
+
+def test_dump_without_iac_files(tmp_path):
+    result = run_dump("-d", str(tmp_path))
+    assert result.returncode != 0
+    assert "No supported IaC files found" in result.stderr + result.stdout