diff --git a/seaice_ecdr/intermediate_monthly.py b/seaice_ecdr/intermediate_monthly.py
index 84b08267..0ebf050f 100644
--- a/seaice_ecdr/intermediate_monthly.py
+++ b/seaice_ecdr/intermediate_monthly.py
@@ -44,6 +44,7 @@
 from seaice_ecdr.constants import DEFAULT_BASE_OUTPUT_DIR
 from seaice_ecdr.days_treated_differently import months_of_cdr_missing_data
 from seaice_ecdr.intermediate_daily import get_ecdr_filepath
+from seaice_ecdr.melt import MELT_SEASON_LAST_DOY
 from seaice_ecdr.nc_attrs import get_global_attrs
 from seaice_ecdr.platforms import PLATFORM_CONFIG, SUPPORTED_PLATFORM_ID
 from seaice_ecdr.tb_data import get_hemisphere_from_crs_da
@@ -471,10 +472,20 @@ def calc_cdr_melt_onset_day_monthly(
 ) -> xr.DataArray:
     """Create the `cdr_melt_onset_day_monthly` variable."""
     # Create `cdr_melt_onset_day_monthly`. This is the value from
-    # the last day of the month.
-    cdr_melt_onset_day_monthly = daily_melt_onset_for_month.sel(
-        time=daily_melt_onset_for_month.time.max()
-    )
+    # the last day of the month unless the month is incomplete.
+    # xarray uses np.datetime64[ns] for time
+    doy_list: list[int] = [
+        int(date.strftime("%j"))
+        for date in daily_melt_onset_for_month.time.dt.date.values
+    ]
+    if MELT_SEASON_LAST_DOY in doy_list:
+        day_244_idx = doy_list.index(MELT_SEASON_LAST_DOY)
+        max_date = daily_melt_onset_for_month.time[day_244_idx].values
+        logger.info(f"Found non-max date with melt: {max_date}")
+    else:
+        max_date = daily_melt_onset_for_month.time.max()
+
+    cdr_melt_onset_day_monthly = daily_melt_onset_for_month.sel(time=max_date)
     cdr_melt_onset_day_monthly.name = "cdr_melt_onset_day_monthly"
     cdr_melt_onset_day_monthly = cdr_melt_onset_day_monthly.drop_vars("time")
 
diff --git a/seaice_ecdr/melt.py b/seaice_ecdr/melt.py
index d8bb6b24..4c2d87a4 100644
--- a/seaice_ecdr/melt.py
+++ b/seaice_ecdr/melt.py
@@ -35,8 +35,8 @@
 import numpy.typing as npt
 
 # Start and end DOYs for the melt season (inclusive)
-MELT_SEASON_FIRST_DOY = 60
-MELT_SEASON_LAST_DOY = 244
+MELT_SEASON_FIRST_DOY: int = 60
+MELT_SEASON_LAST_DOY: int = 244
 
 # Flag value for grid cells before melting is detected or if no melt is ever
 # detected.
diff --git a/seaice_ecdr/tests/unit/test_monthly.py b/seaice_ecdr/tests/unit/test_monthly.py
index 901f3b46..5e6fc267 100644
--- a/seaice_ecdr/tests/unit/test_monthly.py
+++ b/seaice_ecdr/tests/unit/test_monthly.py
@@ -505,7 +505,14 @@ def test_calc_cdr_melt_onset_day_monthly():
         data=_mock_data,
         dims=["y", "time"],
         coords=dict(
-            time=[dt.date(2022, 3, 1), dt.date(2022, 3, 2), dt.date(2022, 3, 3)],
+            time=[
+                np.datetime64(date)
+                for date in [
+                    dt.date(2022, 3, 1),
+                    dt.date(2022, 3, 2),
+                    dt.date(2022, 3, 3),
+                ]
+            ],
             y=list(range(5)),
         ),
     )