diff --git a/src/NmeaParser/Nmea/Gsv.cs b/src/NmeaParser/Nmea/Gsv.cs
index dfd6730..f4a67b9 100644
--- a/src/NmeaParser/Nmea/Gsv.cs
+++ b/src/NmeaParser/Nmea/Gsv.cs
@@ -98,8 +98,10 @@ namespace NmeaParser.Nmea
         internal SatelliteVehicle(string[] message, int startIndex)
         {
             PrnNumber = int.Parse(message[startIndex], CultureInfo.InvariantCulture);
-            Elevation = double.Parse(message[startIndex + 1], CultureInfo.InvariantCulture);
-            Azimuth = double.Parse(message[startIndex + 2], CultureInfo.InvariantCulture);
+            if (double.TryParse(message[startIndex + 1], NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out double e))
+                Elevation = e;
+            if (double.TryParse(message[startIndex + 2], NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out double a))
+                Azimuth = a;
             int snr = -1;
             if (int.TryParse(message[startIndex + 3], out snr))
                 SignalToNoiseRatio = snr;
@@ -111,15 +113,15 @@ namespace NmeaParser.Nmea
         /// <summary>
         /// Elevation in degrees, 90 maximum
         /// </summary>
-        public double Elevation { get; }
+        public double Elevation { get; } = double.NaN;
         /// <summary>
         /// Azimuth, degrees from true north, 000 to 359
         /// </summary>
-        public double Azimuth { get; }
+        public double Azimuth { get; } = double.NaN;
         /// <summary>
         /// Signal-to-Noise ratio, 0-99 dB (-1 when not tracking) 
         /// </summary>
-        public int SignalToNoiseRatio { get; }
+        public int SignalToNoiseRatio { get; } = -1;
 
         /// <summary>
         /// Satellite system
diff --git a/src/UnitTests/NmeaParser.Tests/NmeaMessages.cs b/src/UnitTests/NmeaParser.Tests/NmeaMessages.cs
index 4baa579..5a46943 100644
--- a/src/UnitTests/NmeaParser.Tests/NmeaMessages.cs
+++ b/src/UnitTests/NmeaParser.Tests/NmeaMessages.cs
@@ -343,6 +343,26 @@ namespace NmeaParser.Tests
             Assert.AreEqual(0, gsv.SVs.Count);
         }
 
+
+        [TestMethod]
+        [WorkItem(53)]
+        public void TestGpgsv_MissingElevationAndAzimuth()
+        {
+            string msgstr = "$GPGSV,3,1,12,02,06,225,16,04,,,40,05,65,251,27,07,40,057,43,0*51";
+            var msg = NmeaMessage.Parse(msgstr);
+            Assert.IsInstanceOfType(msg, typeof(Gsv));
+            Gsv gsv = (Gsv)msg;
+            Assert.AreEqual(3, gsv.TotalMessages);
+            Assert.AreEqual(1, gsv.MessageNumber);
+            Assert.AreEqual(12, gsv.SVsInView);
+            Assert.IsNotNull(gsv.SVs);
+            Assert.AreEqual(4, gsv.SVs.Count);
+            Assert.AreEqual(4, gsv.SVs[1].PrnNumber);
+            Assert.IsTrue(double.IsNaN(gsv.SVs[1].Elevation));
+            Assert.IsTrue(double.IsNaN(gsv.SVs[1].Azimuth));
+            Assert.AreEqual(40, gsv.SVs[1].SignalToNoiseRatio);
+        }
+
         [TestMethod]
         public void TestGpgll()
         {