diff --git a/imap_processing/glows/l1a/glows_l1a.py b/imap_processing/glows/l1a/glows_l1a.py
index 4314ce4a85..051b6f6667 100644
--- a/imap_processing/glows/l1a/glows_l1a.py
+++ b/imap_processing/glows/l1a/glows_l1a.py
@@ -338,6 +338,25 @@ def generate_histogram_dataset(
         )
     hist_l1a_list = valid_hists
 
+    # Deduplicate by (imap_start_time, imap_time_offset), keeping the first occurrence.
+    seen_times: dict = {}
+    for hist in hist_l1a_list:
+        key = (
+            hist.imap_start_time.seconds,
+            hist.imap_start_time.subseconds,
+            hist.imap_time_offset.seconds,
+            hist.imap_time_offset.subseconds,
+        )
+        if key not in seen_times:
+            seen_times[key] = hist
+    dedup_hists = list(seen_times.values())
+    if len(dedup_hists) < len(hist_l1a_list):
+        logger.warning(
+            f"GLOWS: Filtered out {len(hist_l1a_list) - len(dedup_hists)} "
+            f"duplicate histogram(s) by imap_start_time and imap_time_offset."
+        )
+    hist_l1a_list = dedup_hists
+
     # Store timestamps for each HistogramL1A object.
     time_data: np.ndarray = np.zeros(len(hist_l1a_list), dtype=np.int64)
     # Data in lists, for each of the 25 time varying datapoints in HistogramL1A
diff --git a/imap_processing/tests/glows/test_glows_l1a_cdf.py b/imap_processing/tests/glows/test_glows_l1a_cdf.py
index d559ae50a7..5e648436ac 100644
--- a/imap_processing/tests/glows/test_glows_l1a_cdf.py
+++ b/imap_processing/tests/glows/test_glows_l1a_cdf.py
@@ -83,6 +83,18 @@ def test_generate_histogram_dataset_filters_zero_imap_start_time(l1a_test_data):
     assert len(dataset["epoch"].values) == 2
 
 
+@pytest.mark.external_test_data
+def test_generate_histogram_dataset_deduplicates(in_flight_packet_path):
+    hist_l0, _ = decom_packets(in_flight_packet_path)
+    hist_l1a = [HistogramL1A(h) for h in hist_l0]
+    glows_attrs = create_glows_attr_obj()
+
+    dataset = generate_histogram_dataset(hist_l1a, glows_attrs)
+
+    epochs = dataset["epoch"].values.tolist()
+    assert len(epochs) == len(set(epochs))
+
+
 def test_generate_de_dataset(l1a_test_data):
     _, de_l1a = l1a_test_data
     glows_attrs = create_glows_attr_obj()