diff --git a/runtime/pb/wire.lua b/runtime/pb/wire.lua
index 62e82c4a489a821201ed9a450c35096f6ddb1e70..a6150a66aa4ecc5b0c98d604106b497b0c73ceda 100644
--- a/runtime/pb/wire.lua
+++ b/runtime/pb/wire.lua
@@ -138,11 +138,15 @@ local function decode_tag(buf, pos)
     local b = buf:byte(pos)
     if b == nil then error("truncated varint at offset " .. pos, 0) end
     if b < 0x80 then
-        return bit.rshift(b, 3), bit.band(b, 7), pos + 1
+        local wt = bit.band(b, 7)
+        if wt >= 6 then error("illegal wire type " .. wt, 0) end
+        return bit.rshift(b, 3), wt, pos + 1
     end
     local v, npos = decode_varint(buf, pos)
     v = tonumber(v)
-    return bit.rshift(v, 3), bit.band(v, 7), npos
+    local wt = bit.band(v, 7)
+    if wt >= 6 then error("illegal wire type " .. wt, 0) end
+    return bit.rshift(v, 3), wt, npos
 end
 M.decode_tag = decode_tag
 
diff --git a/test/conformance/known_failures.txt b/test/conformance/known_failures.txt
index 4d6465b4c719ad7ea870d5e8de65d1fd807fea59..e15f5793a5132a4e5a82340d6394ec32a927c14a 100644
--- a/test/conformance/known_failures.txt
+++ b/test/conformance/known_failures.txt
@@ -80,29 +80,5 @@ Required.Proto3.ProtobufInput.PrematureEofInsideUnknownValue.FLOAT
 Required.Proto3.ProtobufInput.PrematureEofInsideUnknownValue.SFIXED32
 Required.Proto3.ProtobufInput.PrematureEofInsideUnknownValue.SFIXED64
 Required.Proto3.ProtobufInput.RepeatedScalarMessageMerge.ProtobufOutput
-Required.Proto3.ProtobufInput.UnknownWireType6_Field1_Version0
-Required.Proto3.ProtobufInput.UnknownWireType6_Field1_Version1
-Required.Proto3.ProtobufInput.UnknownWireType6_Field1_Version2
-Required.Proto3.ProtobufInput.UnknownWireType6_Field1_Version3
-Required.Proto3.ProtobufInput.UnknownWireType6_Field2_Version0
-Required.Proto3.ProtobufInput.UnknownWireType6_Field2_Version1
-Required.Proto3.ProtobufInput.UnknownWireType6_Field2_Version2
-Required.Proto3.ProtobufInput.UnknownWireType6_Field2_Version3
-Required.Proto3.ProtobufInput.UnknownWireType6_Field3_Version0
-Required.Proto3.ProtobufInput.UnknownWireType6_Field3_Version1
-Required.Proto3.ProtobufInput.UnknownWireType6_Field3_Version2
-Required.Proto3.ProtobufInput.UnknownWireType6_Field3_Version3
-Required.Proto3.ProtobufInput.UnknownWireType7_Field1_Version0
-Required.Proto3.ProtobufInput.UnknownWireType7_Field1_Version1
-Required.Proto3.ProtobufInput.UnknownWireType7_Field1_Version2
-Required.Proto3.ProtobufInput.UnknownWireType7_Field1_Version3
-Required.Proto3.ProtobufInput.UnknownWireType7_Field2_Version0
-Required.Proto3.ProtobufInput.UnknownWireType7_Field2_Version1
-Required.Proto3.ProtobufInput.UnknownWireType7_Field2_Version2
-Required.Proto3.ProtobufInput.UnknownWireType7_Field2_Version3
-Required.Proto3.ProtobufInput.UnknownWireType7_Field3_Version0
-Required.Proto3.ProtobufInput.UnknownWireType7_Field3_Version1
-Required.Proto3.ProtobufInput.UnknownWireType7_Field3_Version2
-Required.Proto3.ProtobufInput.UnknownWireType7_Field3_Version3
 Required.Proto3.ProtobufInput.ValidDataOneof.MESSAGE.Merge.ProtobufOutput
 Required.Proto3.TimestampProtoNegativeNanos.JsonOutput