diff --git a/dlls/msasn1/main.c b/dlls/msasn1/main.c
index c96be7d07d6..d1513629057 100644
--- a/dlls/msasn1/main.c
+++ b/dlls/msasn1/main.c
@@ -190,3 +190,21 @@ void WINAPI ASN1_CloseDecoder(ASN1decoding_t decoder)
 {
     FIXME("(%p): Stub!\n", decoder);
 }
+
+ASN1error_e WINAPI ASN1_Decode(ASN1decoding_t decoder, void **outdata, ASN1uint32_t pdunum,
+                               ASN1uint32_t flags, ASN1octet_t *buf, ASN1uint32_t bufsize)
+{
+    FIXME("(%p %p %u %08x %p %u): Stub!\n", decoder, outdata, pdunum, flags, buf, bufsize);
+
+    if (!decoder)
+        return ASN1_ERR_BADARGS;
+
+    if (!buf || !bufsize)
+    {
+        decoder->err = ASN1_ERR_BADARGS;
+        return ASN1_ERR_BADARGS;
+    }
+
+    decoder->err = ASN1_ERR_BADPDU;
+    return ASN1_ERR_BADPDU;
+}
diff --git a/dlls/msasn1/msasn1.spec b/dlls/msasn1/msasn1.spec
index f98a4a62d7a..ab823b03c31 100644
--- a/dlls/msasn1/msasn1.spec
+++ b/dlls/msasn1/msasn1.spec
@@ -224,7 +224,7 @@
 @ stub ASN1_CreateDecoderEx
 @ stdcall ASN1_CreateEncoder(ptr ptr ptr long ptr)
 @ stdcall ASN1_CreateModule(long long long long ptr ptr ptr ptr long)
-@ stub ASN1_Decode
+@ stdcall ASN1_Decode(ptr ptr long long ptr long)
 @ stub ASN1_Encode
 @ stub ASN1_FreeDecoded
 @ stub ASN1_FreeEncoded