diff --git a/src/Nonemm.Session/QtcTraffic.cs b/src/Nonemm.Session/QtcTraffic.cs
index 2897be8..793a947 100644
--- a/src/Nonemm.Session/QtcTraffic.cs
+++ b/src/Nonemm.Session/QtcTraffic.cs
@@ -214,16 +214,23 @@ public sealed class QtcTraffic
 
     /// The header a station sends in front of a series: a series number, a
     /// separator and how many lines follow. Anything between the two numbers
-    /// counts as the separator, because it is copied off the air.
+    /// counts as the separator, because it is copied off the air. A series
+    /// number on its own means ten lines, which is what N1MM assumes: "If he
+    /// only types the batch number without the forward slash and count, the
+    /// program will assume the count is 10."
     public static (int Series, int Count)? ReadHeader(string text)
     {
         string[] parts = text.Trim().ToUpperInvariant().Replace("QTC", "").Trim()
             .Split(['/', '-', ' ', '\\'], StringSplitOptions.RemoveEmptyEntries);
-        return parts.Length >= 2
-            && int.TryParse(parts[0], out int series)
-            && int.TryParse(parts[1], out int count)
-            && series > 0
-            && count is > 0 and <= WaeQtc.MostPerSeries
+        if (parts.Length == 0 || !int.TryParse(parts[0], out int series) || series <= 0)
+        {
+            return null;
+        }
+        if (parts.Length == 1)
+        {
+            return (series, WaeQtc.MostPerSeries);
+        }
+        return int.TryParse(parts[1], out int count) && count is > 0 and <= WaeQtc.MostPerSeries
             ? (series, count)
             : null;
     }
diff --git a/tests/Nonemm.Session.Tests/QtcTrafficTests.cs b/tests/Nonemm.Session.Tests/QtcTrafficTests.cs
index 8abcdbf..4976e9b 100644
--- a/tests/Nonemm.Session.Tests/QtcTrafficTests.cs
+++ b/tests/Nonemm.Session.Tests/QtcTrafficTests.cs
@@ -314,9 +314,21 @@ public class QtcTrafficTests
         Assert.Equal(10, count);
     }
 
+    /// N1MM fills in the count when the operator types the series number
+    /// alone, because ten is the usual series.
+    [Theory]
+    [InlineData("87")]
+    [InlineData("QTC 87")]
+    public void ASeriesNumberOnItsOwnMeansTenLines(string text)
+    {
+        (int series, int count) = Assert.IsType<(int, int)>(QtcTraffic.ReadHeader(text));
+
+        Assert.Equal(87, series);
+        Assert.Equal(10, count);
+    }
+
     [Theory]
     [InlineData("")]
-    [InlineData("87")]
     [InlineData("87/11")]
     [InlineData("abc/10")]
     public void AHeaderThatIsNotOneReadsAsNothing(string text) =>