diff --git a/daemon/nfs41_daemon.c b/daemon/nfs41_daemon.c
index 2955f96..bcd2da5 100644
--- a/daemon/nfs41_daemon.c
+++ b/daemon/nfs41_daemon.c
@@ -128,7 +128,7 @@ static unsigned int WINAPI thread_main(void *args)
         status = upcall_handle(&upcall);
 
 write_downcall:
-        dprintf(1, "writing downcall: xid=%d opcode=%s status=%d "
+        dprintf(1, "writing downcall: xid=%lld opcode=%s status=%d "
             "get_last_error=%d\n", upcall.xid, opcode2string(upcall.opcode),
             upcall.status, upcall.last_error);
 
@@ -138,7 +138,7 @@ write_downcall:
         status = DeviceIoControl(pipe, IOCTL_NFS41_WRITE,
             inbuf, inbuf_len, NULL, 0, (LPDWORD)&outbuf_len, NULL);
         if (!status) {
-            eprintf("IOCTL_NFS41_WRITE failed with %d xid=%d opcode=%s\n", 
+            eprintf("IOCTL_NFS41_WRITE failed with %d xid=%lld opcode=%s\n", 
                 GetLastError(), upcall.xid, opcode2string(upcall.opcode));
             upcall_cancel(&upcall);
         }
diff --git a/daemon/upcall.c b/daemon/upcall.c
index 5f7eb8b..dcd6a7e 100644
--- a/daemon/upcall.c
+++ b/daemon/upcall.c
@@ -95,7 +95,7 @@ int upcall_parse(
     /* parse common elements */
     status = safe_read(&buffer, &length, &version, sizeof(uint32_t));
     if (status) goto out;
-    status = safe_read(&buffer, &length, &upcall->xid, sizeof(uint32_t));
+    status = safe_read(&buffer, &length, &upcall->xid, sizeof(uint64_t));
     if (status) goto out;
     status = safe_read(&buffer, &length, &upcall->opcode, sizeof(uint32_t));
     if (status) goto out;
diff --git a/daemon/upcall.h b/daemon/upcall.h
index 4cc061a..e276f27 100644
--- a/daemon/upcall.h
+++ b/daemon/upcall.h
@@ -184,7 +184,7 @@ typedef union __upcall_args {
 } upcall_args;
 
 typedef struct __nfs41_upcall {
-    uint32_t                xid;
+    uint64_t                xid;
     uint32_t                opcode;
     uint32_t                status;
     uint32_t                last_error;
diff --git a/sys/nfs41_debug.c b/sys/nfs41_debug.c
index a542fb7..7c3fe87 100644
--- a/sys/nfs41_debug.c
+++ b/sys/nfs41_debug.c
@@ -666,12 +666,12 @@ void print_open_error(int on, int status)
 }
 
 void print_wait_status(int on, const char *prefix, NTSTATUS status, 
-                       const char *opcode, PVOID entry, int xid)
+                       const char *opcode, PVOID entry, LONGLONG xid)
 {
     switch (status) {
     case STATUS_SUCCESS:
         if (opcode)
-            DbgP("%s Got a wakeup call, finishing %s entry=%p xid=%d\n", 
+            DbgP("%s Got a wakeup call, finishing %s entry=%p xid=%lld\n", 
                 prefix, opcode, entry, xid);
         else
             DbgP("%s Got a wakeup call\n", prefix);
diff --git a/sys/nfs41_debug.h b/sys/nfs41_debug.h
index 4402361..2c39ac1 100644
--- a/sys/nfs41_debug.h
+++ b/sys/nfs41_debug.h
@@ -56,7 +56,7 @@ void print_caching_level(int on, ULONG flag);
 const char *opcode2string(int opcode);
 void print_open_error(int on, int status);
 void print_wait_status(int on, const char *str, NTSTATUS status, 
-                       const char *opcode, PVOID entry, int xid);
+                       const char *opcode, PVOID entry, LONGLONG xid);
 void print_acl_args(SECURITY_INFORMATION info);
 
 #define DbgEn() DbgPrintEx(DPFLTR_IHVNETWORK_ID, DPFLTR_ERROR_LEVEL, \
diff --git a/sys/nfs41_driver.c b/sys/nfs41_driver.c
index 9c1d747..5ccbdba 100644
--- a/sys/nfs41_driver.c
+++ b/sys/nfs41_driver.c
@@ -70,7 +70,7 @@ FAST_MUTEX upcallLock, downcallLock;
 FAST_MUTEX xidLock;
 FAST_MUTEX openOwnerLock;
 
-ULONG xid = 0;
+LONGLONG xid = 0;
 ULONG open_owner_id = 1;
 
 #define DECLARE_CONST_ANSI_STRING(_var, _string) \
@@ -122,7 +122,7 @@ typedef enum _nfs41_updowncall_state {
 
 typedef struct _updowncall_entry {
     DWORD version;
-    DWORD xid;
+    LONGLONG xid;
     DWORD opcode;
     NTSTATUS status;
     nfs41_updowncall_state state;
@@ -420,15 +420,6 @@ nfs41_start_driver_state nfs41_start_state = NFS41_START_DRIVER_STARTABLE;
 
 NTSTATUS map_readwrite_errors(DWORD status);
 
-ULONG get_next_xid() 
-{
-    ULONG x;
-    ExAcquireFastMutex(&xidLock);
-    x = ++xid;
-    ExReleaseFastMutex(&xidLock);
-    return x; 
-}
-
 ULONG get_next_open_owner() 
 {
     ULONG x;
@@ -525,7 +516,7 @@ NTSTATUS marshal_nfs41_header(
     RtlCopyMemory(tmp, &entry->open_state, sizeof(HANDLE));
     tmp += sizeof(HANDLE);
 
-    DbgP("[upcall] entry=%p xid=%d opcode=%d version=%d session=0x%x "
+    DbgP("[upcall] entry=%p xid=%lld opcode=%d version=%d session=0x%x "
         "open_state=0x%x\n", entry, entry->xid, entry->opcode, entry->version,
         entry->session, entry->open_state);
 out:
@@ -1348,7 +1339,7 @@ NTSTATUS nfs41_UpcallCreate(
     }
 
     RtlZeroMemory(entry, sizeof(nfs41_updowncall_entry));
-    entry->xid = get_next_xid();
+    entry->xid = InterlockedIncrement64(&xid);
     entry->opcode = opcode;
     entry->state = NFS41_WAITING_FOR_UPCALL;
     entry->session = session;
@@ -1391,7 +1382,7 @@ NTSTATUS nfs41_UpcallWaitForReply(
 
     nfs41_AddEntry(upcallLock, upcall, entry);
     KeSetEvent(&upcallEvent, 0, FALSE);
-    DbgP("@@@ Creating %s upcall entry=%p xid=%d\n", opstring, entry, entry->xid);
+    DbgP("@@@ Creating %s upcall entry=%p xid=%lld\n", opstring, entry, entry->xid);
     if (!entry->async_op) {
         /* 02/03/2011 AGLO: it is not clear what the "right" waiting design 
          * should be. Having non-interruptable waiting seems to be the right 
@@ -1428,12 +1419,12 @@ NTSTATUS nfs41_UpcallWaitForReply(
     default:
         ExAcquireFastMutex(&entry->lock);
         if (entry->state == NFS41_DONE_PROCESSING) {
-            DbgP("[downcall] finish processing %s entry=%p xid=%d\n", 
+            DbgP("[downcall] finish processing %s entry=%p xid=%lld\n", 
                 opcode2string(entry->opcode), entry, entry->xid);
             ExReleaseFastMutex(&entry->lock);
             break;
         }
-        DbgP("[upcall] abandoning %s entry=%p xid=%d\n", 
+        DbgP("[upcall] abandoning %s entry=%p xid=%lld\n", 
             opcode2string(entry->opcode), entry, entry->xid);
         entry->state = NFS41_NOT_WAITING;
         ExReleaseFastMutex(&entry->lock);
@@ -1520,7 +1511,7 @@ NTSTATUS nfs41_downcall(
     buf += sizeof(tmp->status);
     RtlCopyMemory(&tmp->errno, buf, sizeof(tmp->errno));
     buf += sizeof(tmp->errno);
-    DbgP("[downcall] xid=%d opcode=%d status=%d errno=%d\n", tmp->xid, 
+    DbgP("[downcall] xid=%lld opcode=%d status=%d errno=%d\n", tmp->xid, 
         tmp->opcode, tmp->status, tmp->errno);
 
     ExAcquireFastMutex(&downcallLock); 
@@ -1529,7 +1520,6 @@ NTSTATUS nfs41_downcall(
     while (pEntry != NULL) {
         cur = (nfs41_updowncall_entry *)CONTAINING_RECORD(pEntry, 
                 nfs41_updowncall_entry, next);
-        DbgP("nfs41_downcall: comparing %d %d\n", cur->xid, tmp->xid);
         if (cur->xid == tmp->xid) {
             found = 1;
             break;
@@ -1543,7 +1533,7 @@ NTSTATUS nfs41_downcall(
     ExReleaseFastMutex(&downcallLock);
     SeStopImpersonatingClient();
     if (!found) {
-        print_error("Didn't find xid=%d entry\n", tmp->xid);
+        print_error("Didn't find xid=%lld entry\n", tmp->xid);
         goto out_free;
     }