diff --git a/apstools/plans/tests/test_issue606.py b/apstools/plans/tests/test_issue606.py
new file mode 100644
index 000000000..6f4d3c4b7
--- /dev/null
+++ b/apstools/plans/tests/test_issue606.py
@@ -0,0 +1,96 @@
+"""
+Issue 606
+
+> While using TuneAxis().tune(), received this message from
+> a tuning scan where fwhm=None. In this case, the scan did
+> not cross the peak.
+
+    Error saving stream PeakStats:
+
+Because fwhm is None.
+"""
+
+from bluesky import RunEngine
+import bluesky.plan_stubs as bps
+from bluesky.callbacks import best_effort
+import databroker
+import dataclasses
+import pytest
+
+from .. import TuneResults
+
+
+IOC = "gp:"
+
+
+@dataclasses.dataclass
+class PeaksStatisticalData:
+    """Statistical data from bec.peaks"""
+
+    x: str = None
+    y: str = None
+    cen: float = None
+    com: float = None
+    fwhm: float = None
+    min: list = None
+    max: list = None
+    crossings: list = None
+    tune_ok: bool = False
+    center: float = None
+    initial_position: float = 0.0
+    final_position: float = 0.0
+
+
+def peak_stats_plan(peaks, stream="primary"):
+    """Bluesky plan that saves PeakStats as a run."""
+    stats = TuneResults("", name="stats")
+    stats.set_stats(peaks)
+    yield from bps.open_run(md={})
+    yield from bps.create(name=stream)
+    yield from bps.read(stats)
+    yield from bps.save()
+    yield from bps.close_run()
+
+
+def test_results_stream(capsys):
+    bec = best_effort.BestEffortCallback()
+    cat = databroker.temp()
+    RE = RunEngine({})
+    RE.subscribe(cat.v1.insert)
+    RE.subscribe(bec)
+
+    peaks = PeaksStatisticalData()
+    peaks.x = "m1"
+    peaks.y = "noisy"
+    peaks.cen = -0.1550618680443165
+    peaks.com = -0.05085308669291895
+    peaks.fwhm = None
+    peaks.min = [6.65000000e-01, 7.08289488e02]
+    peaks.max = [-3.35000000e-01, 6.30815141e03]
+    peaks.crossings = [-0.15506187]
+    peaks.tune_ok = True
+    peaks.center = -0.1550618680443165
+    peaks.initial_position = 0.165
+    peaks.final_position = -0.1550618680443165
+
+    RE(peak_stats_plan(peaks, "PeakStats"))
+    out, err = capsys.readouterr()
+    assert err == ""
+    assert out.find("PeakStats") >= 0
+
+    run = cat.v2[-1]
+    assert "PeakStats" in run
+    assert run.metadata["start"]["scan_id"] == 1
+
+    ds = run.PeakStats.read()
+    prefix = "stats_"
+    assert ds[f"{prefix}x"].data[0] == "m1"
+    assert ds[f"{prefix}y"].data[0] == "noisy"
+    assert ds[f"{prefix}fwhm"].data[0] == "null"
+    assert ds[f"{prefix}cen"].data[0] == -0.1550618680443165
+    assert ds[f"{prefix}com"].data[0] == -0.05085308669291895
+    assert ds[f"{prefix}crossings"].data[0] == [-0.15506187]
+
+    # these keys are not written by TuneResults.set_stats()
+    for k in "center tune_ok initial_position final_position".split():
+        assert ds[f"{prefix}{k}"].data[0] == 0
diff --git a/pytest.ini b/pytest.ini
index 52fe7487f..51237018d 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -4,3 +4,4 @@ filterwarnings =
     ignore:.*imp module is deprecated in favour of importlib:DeprecationWarning
     ignore:.*will be removed in a future release.:DeprecationWarning
     ignore:.*DataFrame is highly fragmented.*:Warning
+    ignore:.*Broker.insert may be removed.*:PendingDeprecationWarning