diff --git a/malariagen_data/anoph/cnv_data.py b/malariagen_data/anoph/cnv_data.py
index 181e1b8b3..06a055e58 100644
--- a/malariagen_data/anoph/cnv_data.py
+++ b/malariagen_data/anoph/cnv_data.py
@@ -745,6 +745,9 @@ def plot_cnv_hmm_coverage_track(
         debug("remove data where HMM is not called")
         data = data.query("call_CN >= 0")
 
+        if len(data) == 0:
+            return None
+
         debug("set up y range")
         if y_max == "auto":
             y_max_float = data["call_CN"].max() + 2