diff --git a/MetadataProcessor.Shared/Tables/nanoSignaturesTable.cs b/MetadataProcessor.Shared/Tables/nanoSignaturesTable.cs
index b75b20b..080ec5e 100644
--- a/MetadataProcessor.Shared/Tables/nanoSignaturesTable.cs
+++ b/MetadataProcessor.Shared/Tables/nanoSignaturesTable.cs
@@ -817,7 +817,15 @@ private void WriteAttributeArgumentValue(
                         break;
                     case NanoCLRDataType.DATATYPE_STRING:
                         writer.Write((byte)nanoSerializationType.ELEMENT_TYPE_STRING);
-                        writer.Write(_context.StringTable.GetOrCreateStringId((string)argument.Value));
+                        if (argument.Value == null)
+                        {
+                            // write sentinel for null string
+                            writer.Write((ushort)0xFFFF);
+                        }
+                        else
+                        {
+                            writer.Write(_context.StringTable.GetOrCreateStringId((string)argument.Value));
+                        }
                         break;
                     default:
                         Debug.Fail(dataType.ToString());
diff --git a/MetadataProcessor.Tests/TestNFApp/MyClass1.cs b/MetadataProcessor.Tests/TestNFApp/MyClass1.cs
index 388cdab..0b54af3 100644
--- a/MetadataProcessor.Tests/TestNFApp/MyClass1.cs
+++ b/MetadataProcessor.Tests/TestNFApp/MyClass1.cs
@@ -31,6 +31,11 @@ public void MyMethodWithData()
         {
         }
 
+        [DataRow(999, null)]
+        public void MyMethodWithDataRowWithNull()
+        {
+        }
+
         private readonly int _myField;
 
         [Ignore("I'm ignoring you!")]