diff --git a/evaluate_egospeak_opportunity_events.py b/evaluate_egospeak_opportunity_events.py
index 788b9c7..c0d8fe6 100755
--- a/evaluate_egospeak_opportunity_events.py
+++ b/evaluate_egospeak_opportunity_events.py
@@ -173,8 +173,8 @@ def _candidate_region(
         field="region_end_seconds",
         uid=uid,
     )
-    if end <= start:
-        raise ValueError(f"{uid}: opportunity region must have positive duration")
+    if end < start:
+        raise ValueError(f"{uid}: opportunity region ends before it starts")
     return start, end
 
 
diff --git a/test_evaluate_egospeak_opportunity_events.py b/test_evaluate_egospeak_opportunity_events.py
index 05741a5..fd74ee3 100644
--- a/test_evaluate_egospeak_opportunity_events.py
+++ b/test_evaluate_egospeak_opportunity_events.py
@@ -183,6 +183,27 @@ class OpportunityEventTests(unittest.TestCase):
             1,
         )
 
+    def test_zero_duration_mined_opportunity_is_skipped_not_fatal(self) -> None:
+        temporary, path = self.write_reviews([
+            reviewed_row(
+                "zero-gap",
+                family="entry",
+                verdict="HARD_NEGATIVE",
+                subtype="ENTRY_OTHER_TO_OTHER",
+                anchor=2.0,
+                region_start=2.0,
+                region_end=2.0,
+                candidate_source="OTHER_TO_OTHER",
+            )
+        ])
+        self.addCleanup(temporary.cleanup)
+        events, diagnostics = load_opportunity_events([path], ["Session_4"])
+        self.assertEqual(events, [])
+        self.assertEqual(
+            diagnostics["skipped"]["entry_nonpositive_opportunity_duration"],
+            1,
+        )
+
     def test_entry_score_uses_max_wearer_probability_before_resolution(self) -> None:
         event = OpportunityEvent(
             "entry", "Session_4", "entry", True, "WEARER_ENTRY", "WEARER_ONSET",