diff --git a/minimateplus/event_file_io.py b/minimateplus/event_file_io.py
index a7980f1..c3d273c 100644
--- a/minimateplus/event_file_io.py
+++ b/minimateplus/event_file_io.py
@@ -811,7 +811,18 @@ def read_blastware_file(path: Union[str, Path]) -> Event:
         project=project, client=client, operator=user, sensor_location=seisloc,
     )
     ev.raw_samples = samples
-    ev.peak_values = _peaks_from_samples(samples)
+    # Only compute peaks from samples when we actually have samples.
+    # For events the codec couldn't decode (histogram-mode bodies, until
+    # the §7.6.2 histogram codec is wired in), samples is an empty dict
+    # and ``_peaks_from_samples`` would return PeakValues(0, 0, 0, 0, 0).
+    # That would then OVERWRITE existing good DB peak values (e.g. from
+    # paired BW ASCII reports) during the backfill UPSERT path.
+    # Leaving peak_values=None signals "we don't know" to downstream
+    # consumers; the backfill script seeds from the DB row when it sees
+    # None, and ``apply_report_to_event`` overlays from a paired ASCII
+    # report when one is supplied.
+    has_samples = any(samples.get(ch) for ch in ("Tran", "Vert", "Long", "MicL"))
+    ev.peak_values = _peaks_from_samples(samples) if has_samples else None
     ev._a5_frames = None  # not recoverable from BW file
 
     return ev
diff --git a/tests/test_event_file_io.py b/tests/test_event_file_io.py
index d8b5793..6e08dae 100644
--- a/tests/test_event_file_io.py
+++ b/tests/test_event_file_io.py
@@ -289,9 +289,15 @@ def test_read_blastware_file_round_trip(tmp_path: Path):
     assert parsed.timestamp.second == ev.timestamp.second
     # No A5 source recoverable.
     assert parsed._a5_frames is None
-    # Peaks computed from samples (synthetic = zero samples → zero peaks).
-    assert parsed.peak_values is not None
-    assert parsed.peak_values.peak_vector_sum == 0.0
+    # The synthetic event has no real waveform body, so the codec can't
+    # decode samples → read_blastware_file leaves peak_values=None
+    # (the "we don't know" signal) rather than fabricating all-zero
+    # peaks that would otherwise overwrite real DB values via UPSERT.
+    assert parsed.peak_values is None
+    assert parsed.raw_samples is not None
+    # Empty channels — codec returned None for the malformed synthetic body.
+    for ch in ("Tran", "Vert", "Long", "MicL"):
+        assert parsed.raw_samples[ch] == []
 
 
 _BW_CODEC_FIXTURES = [