diff --git a/reflect/CustomAttributeData.cs b/reflect/CustomAttributeData.cs
index b9574d56..9da38ce6 100644
--- a/reflect/CustomAttributeData.cs
+++ b/reflect/CustomAttributeData.cs
@@ -412,7 +412,7 @@ private static CustomAttributeTypedArgument ReadFixedArg(Module context, ByteRea
 			}
 			else
 			{
-				throw new InvalidOperationException();
+				throw new InvalidOperationException(type.ToString());
 			}
 		}
 
diff --git a/reflect/Metadata/Tables.cs b/reflect/Metadata/Tables.cs
index 75ceef7c..491c1ba1 100644
--- a/reflect/Metadata/Tables.cs
+++ b/reflect/Metadata/Tables.cs
@@ -1244,6 +1244,8 @@ internal static int EncodeHasCustomAttribute(int token)
 					return (token & 0xFFFFFF) << 5 | 18;
 				case GenericParamTable.Index:
 					return (token & 0xFFFFFF) << 5 | 19;
+				case GenericParamConstraintTable.Index:
+					return (token & 0xFFFFFF) << 5 | 20;
 				default:
 					throw new InvalidOperationException();
 			}
diff --git a/reflect/Reader/MetadataReader.cs b/reflect/Reader/MetadataReader.cs
index 28a4720d..7d7cf669 100644
--- a/reflect/Reader/MetadataReader.cs
+++ b/reflect/Reader/MetadataReader.cs
@@ -226,6 +226,8 @@ internal int ReadHasCustomAttribute()
 					return (ManifestResourceTable.Index << 24) + (codedIndex >> 5);
 				case 19:
 					return (GenericParamTable.Index << 24) + (codedIndex >> 5);
+				case 20:
+					return (GenericParamConstraintTable.Index << 24) + (codedIndex >> 5);
 				default:
 					throw new BadImageFormatException();
 			}