diff --git a/src/layup/orbitfit.py b/src/layup/orbitfit.py
index afab1db..c09b454 100644
--- a/src/layup/orbitfit.py
+++ b/src/layup/orbitfit.py
@@ -516,7 +516,7 @@ def _orbitfit(
 
         # Check if certain columns are present in the data
         column_names = data.dtype.names
-        g_column_present = "astCat" in column_names
+        astcat_column_present = "astCat" in column_names
         program_column_present = "program" in column_names
         position_rates_columns_present = all(col in column_names for col in ["raRate", "decRate"])
 
@@ -566,15 +566,19 @@ def _orbitfit(
                 )
 
             if weight_data:
-                data_weight = data_weight_Veres2017(
+                # data_weight_Veres2017 returns the astrometric uncertainty in
+                # ARCSECONDS (per its docstring), but Observation.ra_unc /
+                # dec_unc are stored in RADIANS.  Convert at the assignment.
+                data_weight_arcsec = data_weight_Veres2017(
                     obsCode=d["stn"],
                     jd_tdb=convert_tdb_date_to_julian_date(d["obsTime"], cache_dir),
                     catalog=d["astCat"] if astcat_column_present else None,
                     program=d["program"] if program_column_present else None,
                 )
+                data_weight_rad = data_weight_arcsec * np.pi / (180.0 * 3600.0)
 
-                o.ra_unc = data_weight
-                o.dec_unc = data_weight
+                o.ra_unc = data_weight_rad
+                o.dec_unc = data_weight_rad
 
             observations.append(o)
 
diff --git a/tests/layup/test_weight_data.py b/tests/layup/test_weight_data.py
new file mode 100644
index 0000000..6c892c7
--- /dev/null
+++ b/tests/layup/test_weight_data.py
@@ -0,0 +1,81 @@
+"""Regression tests for `orbitfit(weight_data=True)`.
+
+Guards two bugs that previously broke the `weight_data=True` code path:
+
+  1. `g_column_present` was defined but `astcat_column_present` was
+     referenced inside _orbitfit, raising NameError at the first
+     data_weight_Veres2017 call -- failure mode: hard crash before
+     any fitting happened.
+
+  2. `data_weight_Veres2017` returns astrometric uncertainty in
+     ARCSECONDS (per its docstring), but the call site assigned the
+     return value directly to Observation.ra_unc / dec_unc which are
+     stored in RADIANS -- failure mode: weights were ~206000x too
+     loose, fit covariance inflated to absurd values (sigma_pos
+     ~25 million km on a 3 AU object), chi-square -> 0.
+
+The fix is a one-line rename plus an explicit arcsec->radian
+conversion at the call site; this file guards against either kind
+of regression.
+"""
+
+from __future__ import annotations
+
+import os
+
+import numpy as np
+import pytest
+
+from layup.orbitfit import orbitfit
+from layup.utilities.data_processing_utilities import parse_cov
+from layup.utilities.data_utilities_for_tests import get_test_filepath
+from layup.utilities.file_io.CSVReader import CSVDataReader
+
+CACHE = os.path.expanduser("~/Library/Caches/layup")
+EPHEM_PLANETS = os.path.join(CACHE, "linux_p1550p2650.440")
+EPHEM_SMALLBODIES = os.path.join(CACHE, "sb441-n16.bsp")
+EPHEM_AVAILABLE = os.path.exists(EPHEM_PLANETS) and os.path.exists(EPHEM_SMALLBODIES)
+AU_KM = 149597870.7
+
+pytestmark = pytest.mark.skipif(
+    not EPHEM_AVAILABLE,
+    reason=f"ASSIST ephemeris missing at {CACHE}; skipping weight_data test.",
+)
+
+
+def _fit_one(prov_id: str, weight_data: bool):
+    reader = CSVDataReader(
+        get_test_filepath("4_random_mpc_ADES_provIDs_no_sats.csv"),
+        "csv",
+        primary_id_column_name="provID",
+    )
+    data = reader.read_rows()
+    data = data[data["provID"] == prov_id]
+    assert len(data) > 0, f"test fixture missing provID {prov_id}"
+    return orbitfit(data, cache_dir=CACHE, weight_data=weight_data)[0]
+
+
+def test_orbitfit_weight_data_true_runs_without_crashing():
+    """orbitfit(weight_data=True) on real MPC data without an astCat column
+    must run to completion -- previously raised NameError on the missing
+    astcat_column_present variable."""
+    row = _fit_one("119839", weight_data=True)
+    assert "flag" in row.dtype.names
+
+
+def test_orbitfit_weight_data_true_gives_sensible_uncertainty():
+    """orbitfit(weight_data=True) must apply weights in the right units.
+    Previously the returned arcsecond value was assigned directly to
+    Observation.ra_unc (which is in radians), inflating sigma_pos by
+    ~5 orders of magnitude.  An explicit cap of 10000 km on the position
+    uncertainty for our well-constrained 27-year mainbelt arc catches
+    that regression: actual sigma_pos with the fix is O(100 km)."""
+    row = _fit_one("119839", weight_data=True)
+    assert row["flag"] == 0, f"weight_data=True fit did not converge (flag={row['flag']})"
+    cov = parse_cov(row)
+    sigma_pos_km = float(np.sqrt(cov[0, 0] + cov[1, 1] + cov[2, 2])) * AU_KM
+    assert sigma_pos_km < 10000.0, (
+        f"sigma_pos={sigma_pos_km:.1f} km is unreasonably large for a "
+        f"587-obs 27-year arc; likely a units regression in the "
+        f"weight assignment (arcsec vs radian)."
+    )