diff --git a/include/wmcodecdsp.idl b/include/wmcodecdsp.idl
index 1e43766a358..809e528d7e2 100644
--- a/include/wmcodecdsp.idl
+++ b/include/wmcodecdsp.idl
@@ -20,6 +20,7 @@ import "mediaobj.idl";
 import "strmif.idl";
 
 cpp_quote("DEFINE_GUID(MEDIASUBTYPE_I420,0x30323449,0x0000,0x0010,0x80,0x00,0x00,0xaa,0x00,0x38,0x9b,0x71);")
+cpp_quote("DEFINE_GUID(MEDIASUBTYPE_MSAUDIO1,0x00000160,0x0000,0x0010,0x80,0x00,0x00,0xaa,0x00,0x38,0x9b,0x71);")
 
 [
     uuid(bbeea841-0a63-4f52-a7ab-a9b3a84ed38a)