diff --git a/src/quetz_client/client.py b/src/quetz_client/client.py
index 0d83592..7e5d2ba 100644
--- a/src/quetz_client/client.py
+++ b/src/quetz_client/client.py
@@ -56,6 +56,16 @@ class Package:
     latest_change: str
 
 
+
+def _assert_file_is_package(file: Path):
+    """Raises an error if the file in question does not look like a conda package"""
+    valid_suffixes =[".tar.bz2", ".conda"]
+    file_has_valid_suffix = any(file.name.endswith(suffix) for suffix in valid_suffixes)
+    if not file_has_valid_suffix:
+        raise ValueError(f"File {file} does not look like a conda package. It should end in one of {valid_suffixes}.")
+
+    return False
+
 @dataclass
 class QuetzClient:
     session: requests.Session
@@ -172,6 +182,9 @@ def yield_packages(
 
     def post_file_to_channel(self, channel: str, file: Path, force: bool = False):
         file_path = Path(file)
+
+        _assert_file_is_package(file_path)
+
         url = f"{self.url}/api/channels/{channel}/upload/{file_path.name}"
         body_bytes = file_path.read_bytes()
 
diff --git a/tests/test_mock.py b/tests/test_mock.py
index a0a3321..924b32d 100644
--- a/tests/test_mock.py
+++ b/tests/test_mock.py
@@ -3,7 +3,7 @@
 from quetz_client.client import QuetzClient
 
 from .conftest import temporary_package_file
-
+from pathlib import Path
 
 @pytest.mark.parametrize(
     "role",
@@ -170,3 +170,16 @@ def test_mock_post_file_to_channel(
     # thus we need to access all the requests
     assert len(requests_mock.request_history) <= 2
     assert any(r.method == "POST" for r in requests_mock.request_history)
+
+
+def test_mock_post_file_to_channel_invalid_file(
+    mock_client: QuetzClient,
+):
+    """Test that the client refuses to upload an invalid file that is not a conda package
+
+    This test requires to mock server because no actual request are ever made.
+    The client should exit before talking to the server.
+    """
+    file = Path("./wrong_suffix.txt")
+    with pytest.raises(ValueError):
+        mock_client.post_file_to_channel(channel="doesnotmatter", file=file)