diff --git a/dlls/secur32/ntlm.c b/dlls/secur32/ntlm.c
index 79241561eb2..5041892f2de 100644
--- a/dlls/secur32/ntlm.c
+++ b/dlls/secur32/ntlm.c
@@ -380,6 +380,26 @@ static int ntlm_GetTokenBufferIndex(PSecBufferDesc pMessage)
     return -1;
 }
 
+/*************************************************************************
+ *             ntlm_GetDataBufferIndex
+ * Calculates the index of the first secbuffer with BufferType == SECBUFFER_DATA
+ * Returns index if found or -1 if not found.
+ */
+static int ntlm_GetDataBufferIndex(PSecBufferDesc pMessage)
+{
+    UINT i;
+
+    TRACE("%p\n", pMessage);
+
+    for( i = 0; i < pMessage->cBuffers; ++i )
+    {
+        if(pMessage->pBuffers[i].BufferType == SECBUFFER_DATA)
+            return i;
+    }
+
+    return -1;
+}
+
 /***********************************************************************
  *              InitializeSecurityContextW
  */
@@ -1609,7 +1629,7 @@ static SECURITY_STATUS SEC_ENTRY ntlm_EncryptMessage(PCtxtHandle phContext,
         ULONG fQOP, PSecBufferDesc pMessage, ULONG MessageSeqNo)
 {
     PNegoHelper helper;
-    int token_idx;
+    int token_idx, data_idx;
 
     TRACE("(%p %d %p %d)\n", phContext, fQOP, pMessage, MessageSeqNo);
 
@@ -1628,6 +1648,9 @@ static SECURITY_STATUS SEC_ENTRY ntlm_EncryptMessage(PCtxtHandle phContext,
     if((token_idx = ntlm_GetTokenBufferIndex(pMessage)) == -1)
         return SEC_E_INVALID_TOKEN;
 
+    if((data_idx = ntlm_GetDataBufferIndex(pMessage)) ==-1 )
+        return SEC_E_INVALID_TOKEN;
+
     if(pMessage->pBuffers[token_idx].cbBuffer < 16)
         return SEC_E_BUFFER_TOO_SMALL;
 
@@ -1638,8 +1661,8 @@ static SECURITY_STATUS SEC_ENTRY ntlm_EncryptMessage(PCtxtHandle phContext,
     { 
         ntlm_CreateSignature(helper, pMessage, token_idx, NTLM_SEND, FALSE);
         SECUR32_arc4Process(helper->crypt.ntlm2.send_a4i,
-                (BYTE *)pMessage->pBuffers[1].pvBuffer,
-                pMessage->pBuffers[1].cbBuffer);
+                (BYTE *)pMessage->pBuffers[data_idx].pvBuffer,
+                pMessage->pBuffers[data_idx].cbBuffer);
 
         if(helper->neg_flags & NTLMSSP_NEGOTIATE_KEY_EXCHANGE)
             SECUR32_arc4Process(helper->crypt.ntlm2.send_a4i,
@@ -1662,8 +1685,9 @@ static SECURITY_STATUS SEC_ENTRY ntlm_EncryptMessage(PCtxtHandle phContext,
 
         sig = pMessage->pBuffers[token_idx].pvBuffer;
 
-        SECUR32_arc4Process(helper->crypt.ntlm.a4i, pMessage->pBuffers[1].pvBuffer,
-                pMessage->pBuffers[1].cbBuffer);
+        SECUR32_arc4Process(helper->crypt.ntlm.a4i,
+                pMessage->pBuffers[data_idx].pvBuffer,
+                pMessage->pBuffers[data_idx].cbBuffer);
         SECUR32_arc4Process(helper->crypt.ntlm.a4i, sig+4, 12);
 
         if(helper->neg_flags & NTLMSSP_NEGOTIATE_ALWAYS_SIGN || helper->neg_flags == 0)
@@ -1683,7 +1707,7 @@ static SECURITY_STATUS SEC_ENTRY ntlm_DecryptMessage(PCtxtHandle phContext,
     SECURITY_STATUS ret;
     ULONG ntlmssp_flags_save;
     PNegoHelper helper;
-    int token_idx;
+    int token_idx, data_idx;
     TRACE("(%p %p %d %p)\n", phContext, pMessage, MessageSeqNo, pfQOP);
 
     if(!phContext)
@@ -1698,6 +1722,9 @@ static SECURITY_STATUS SEC_ENTRY ntlm_DecryptMessage(PCtxtHandle phContext,
     if((token_idx = ntlm_GetTokenBufferIndex(pMessage)) == -1)
         return SEC_E_INVALID_TOKEN;
 
+    if((data_idx = ntlm_GetDataBufferIndex(pMessage)) ==-1)
+        return SEC_E_INVALID_TOKEN;
+
     if(pMessage->pBuffers[token_idx].cbBuffer < 16)
         return SEC_E_BUFFER_TOO_SMALL;
 
@@ -1706,12 +1733,14 @@ static SECURITY_STATUS SEC_ENTRY ntlm_DecryptMessage(PCtxtHandle phContext,
     if(helper->neg_flags & NTLMSSP_NEGOTIATE_NTLM2 && helper->neg_flags & NTLMSSP_NEGOTIATE_SEAL)
     {
         SECUR32_arc4Process(helper->crypt.ntlm2.recv_a4i,
-                pMessage->pBuffers[1].pvBuffer, pMessage->pBuffers[1].cbBuffer);
+                pMessage->pBuffers[data_idx].pvBuffer,
+                pMessage->pBuffers[data_idx].cbBuffer);
     }
     else
     {
         SECUR32_arc4Process(helper->crypt.ntlm.a4i,
-                pMessage->pBuffers[1].pvBuffer, pMessage->pBuffers[1].cbBuffer);
+                pMessage->pBuffers[data_idx].pvBuffer,
+                pMessage->pBuffers[data_idx].cbBuffer);
     }
 
     /* Make sure we use a session key for the signature check, EncryptMessage