diff --git a/NetCore8583.Test/NetCore8583.Test.csproj b/NetCore8583.Test/NetCore8583.Test.csproj
index e0c7f91..643dfb8 100644
--- a/NetCore8583.Test/NetCore8583.Test.csproj
+++ b/NetCore8583.Test/NetCore8583.Test.csproj
@@ -73,6 +73,9 @@
     <None Update="Resources\radix.xml">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="Resources\issue15.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
   </ItemGroup>
 
 </Project>
diff --git a/NetCore8583.Test/Resources/issue15.xml b/NetCore8583.Test/Resources/issue15.xml
new file mode 100644
index 0000000..abc85a8
--- /dev/null
+++ b/NetCore8583.Test/Resources/issue15.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!-- Config for issue 15: conditional fields beyond bit 64 (no secondary bitmap in message) -->
+<n8583-config>
+    <parse type="9800">
+        <field num="24" type="NUMERIC" length="3" />
+        <field num="31" type="LLVAR" />
+        <field num="125" type="LLVAR" />
+    </parse>
+</n8583-config>
diff --git a/NetCore8583.Test/TestIssue15.cs b/NetCore8583.Test/TestIssue15.cs
new file mode 100644
index 0000000..0aafc37
--- /dev/null
+++ b/NetCore8583.Test/TestIssue15.cs
@@ -0,0 +1,92 @@
+using NetCore8583.Extensions;
+using NetCore8583.Parse;
+using Xunit;
+
+namespace NetCore8583.Test
+{
+    /// <summary>
+    /// Tests for issue #15: conditional fields beyond bit 64 when secondary bitmap is absent.
+    /// When a parse template defines fields > 64 (e.g. field 125) but a message only contains
+    /// fields within the primary bitmap, parsing must not throw.
+    /// </summary>
+    public class TestIssue15
+    {
+        // Message type 9800 as ASCII: '9','8','0','0'
+        private static readonly byte[] Mti = { 0x39, 0x38, 0x30, 0x30 };
+
+        // Primary-only BCD bitmap: bit 24 (field 24) and bit 31 (field 31) set, bit 1 = 0 (no secondary)
+        // Byte 3 (bits 17-24): 0x01 sets bit 24
+        // Byte 4 (bits 25-32): 0x02 sets bit 31
+        private static readonly byte[] PrimaryBitmap = { 0x00, 0x00, 0x01, 0x02, 0x00, 0x00, 0x00, 0x00 };
+
+        // Primary bitmap with secondary indicator: same as above but bit 1 (MSB of byte 1) = 1
+        private static readonly byte[] PrimaryBitmapWithSecondary = { 0x80, 0x00, 0x01, 0x02, 0x00, 0x00, 0x00, 0x00 };
+
+        // Secondary bitmap: only bit 125 set.
+        // Bit 125 is in secondary byte 8 (bits 121-128): value 0x08
+        private static readonly byte[] SecondaryBitmapWith125 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08 };
+
+        // Field 24 NUMERIC n3: "089"
+        private static readonly byte[] Field24 = { 0x30, 0x38, 0x39 };
+
+        // Field 31 LLVAR: length "02", data "AB"
+        private static readonly byte[] Field31 = { 0x30, 0x32, 0x41, 0x42 };
+
+        // Field 125 LLVAR: length "03", data "XYZ"
+        private static readonly byte[] Field125 = { 0x30, 0x33, 0x58, 0x59, 0x5A };
+
+        private static sbyte[] BuildMessage(params byte[][] parts)
+        {
+            var totalLength = 0;
+            foreach (var part in parts) totalLength += part.Length;
+            var buf = new byte[totalLength];
+            var pos = 0;
+            foreach (var part in parts)
+            {
+                part.CopyTo(buf, pos);
+                pos += part.Length;
+            }
+            return buf.ToInt8();
+        }
+
+        [Fact]
+        public void TestConditionalField125_NoPrimaryBitmapAbsent_ShouldParseWithoutCrash()
+        {
+            // Field 125 is in the parse template but the message has no secondary bitmap.
+            // Parsing must succeed and field 125 must not be present in the result.
+            var mf = new MessageFactory<IsoMessage> { UseBinaryBitmap = true };
+            ConfigParser.ConfigureFromClasspathConfig(mf, @"/Resources/issue15.xml");
+
+            var buf = BuildMessage(Mti, PrimaryBitmap, Field24, Field31);
+            var msg = mf.ParseMessage(buf, 0);
+
+            Assert.NotNull(msg);
+            Assert.Equal(0x9800, msg.Type);
+            Assert.True(msg.HasField(24), "Field 24 should be present");
+            Assert.True(msg.HasField(31), "Field 31 should be present");
+            Assert.False(msg.HasField(125), "Field 125 should be absent when secondary bitmap is not present");
+            Assert.Equal("089", msg.GetField(24).ToString());
+            Assert.Equal("AB", msg.GetField(31).ToString());
+        }
+
+        [Fact]
+        public void TestConditionalField125_SecondaryBitmapPresent_ShouldParseField125()
+        {
+            // Field 125 is in the parse template and the message has a secondary bitmap with bit 125 set.
+            var mf = new MessageFactory<IsoMessage> { UseBinaryBitmap = true };
+            ConfigParser.ConfigureFromClasspathConfig(mf, @"/Resources/issue15.xml");
+
+            var buf = BuildMessage(Mti, PrimaryBitmapWithSecondary, SecondaryBitmapWith125, Field24, Field31, Field125);
+            var msg = mf.ParseMessage(buf, 0);
+
+            Assert.NotNull(msg);
+            Assert.Equal(0x9800, msg.Type);
+            Assert.True(msg.HasField(24), "Field 24 should be present");
+            Assert.True(msg.HasField(31), "Field 31 should be present");
+            Assert.True(msg.HasField(125), "Field 125 should be present when secondary bitmap is set");
+            Assert.Equal("089", msg.GetField(24).ToString());
+            Assert.Equal("AB", msg.GetField(31).ToString());
+            Assert.Equal("XYZ", msg.GetField(125).ToString());
+        }
+    }
+}