diff --git a/oscar/SleepLib/loader_plugins/prs1_loader.cpp b/oscar/SleepLib/loader_plugins/prs1_loader.cpp
index 5353de52..8804750e 100644
--- a/oscar/SleepLib/loader_plugins/prs1_loader.cpp
+++ b/oscar/SleepLib/loader_plugins/prs1_loader.cpp
@@ -7221,12 +7221,6 @@ bool PRS1Import::ParseSession(void)
             break;
         }
         
-        // If there's nothing beyond the compliance or summary (no event or waveform data), mark this session as
-        // a summary.
-        if (m_event_chunks.count() == 0 && m_wavefiles.isEmpty() && oxifile.isEmpty()) {
-            session->setSummaryOnly(true);
-        }
-
         // Import the slices into the session
         for (auto & slice : m_slices) {
             // Filter out 0-length slices, since they cause problems for Day::total_time().
@@ -7241,6 +7235,14 @@ bool PRS1Import::ParseSession(void)
             }
         }
         
+        // If are no mask-on slices, then there's not any meaningful event or waveform data for the session.
+        // If there's no no event or waveform data, mark this session as a summary.
+        if (session->m_slices.count() == 0 || (m_event_chunks.count() == 0 && m_wavefiles.isEmpty() && oxifile.isEmpty())) {
+            session->setSummaryOnly(true);
+            save = true;
+            break;  // and skip the occasional fragmentary event or waveform data
+        }
+
         // TODO: There should be a way to distinguish between no-data-to-import vs. parsing errors
         // (once we figure out what's benign and what isn't).
         if (m_event_chunks.count() > 0) {
diff --git a/oscar/tests/sessiontests.cpp b/oscar/tests/sessiontests.cpp
index 4ba5838c..303984e9 100644
--- a/oscar/tests/sessiontests.cpp
+++ b/oscar/tests/sessiontests.cpp
@@ -195,10 +195,14 @@ void SessionToYaml(QString filepath, Session* session, bool ok)
             out << "    end: " << ts(slice.end) << endl;
         }
     }
-    Day day;
-    day.addSession(session);
-    out << "  total_time: " << dur(day.total_time()) << endl;
-    day.removeSession(session);
+    qint64 total_time = 0;
+    if (session->first() != 0) {
+        Day day;
+        day.addSession(session);
+        total_time = day.total_time();
+        day.removeSession(session);
+    }
+    out << "  total_time: " << dur(total_time) << endl;
 
     out << "  settings:" << endl;