diff --git a/daemon/lock.c b/daemon/lock.c
index 5044259..1386577 100644
--- a/daemon/lock.c
+++ b/daemon/lock.c
@@ -155,6 +155,13 @@ static int handle_lock(nfs41_upcall *upcall)
 
     nfs41_lock_stateid_arg(state, &stateid);
 
+    /* 18.10.3. Operation 12: LOCK - Create Lock
+     * "To lock the file from a specific offset through the end-of-file
+     * (no matter how long the file actually is) use a length field equal
+     * to NFS4_UINT64_MAX." */
+    if (args->length >= NFS4_UINT64_MAX - args->offset)
+        args->length = NFS4_UINT64_MAX;
+
     status = nfs41_lock(state->session, &state->file, &state->owner,
         type, args->offset, args->length, FALSE, TRUE, &stateid);
     if (status) {
@@ -240,6 +247,10 @@ static int handle_unlock(nfs41_upcall *upcall)
         if (safe_read(&buf, &buf_len, &offset, sizeof(LONGLONG))) break;
         if (safe_read(&buf, &buf_len, &length, sizeof(LONGLONG))) break;
 
+        /* do the same translation as LOCK, or the ranges won't match */
+        if (length >= NFS4_UINT64_MAX - offset)
+            length = NFS4_UINT64_MAX;
+
         status = nfs41_unlock(state->session,
             &state->file, offset, length, &stateid);
         if (status == NFS4_OK) {
diff --git a/daemon/upcall.h b/daemon/upcall.h
index 2b1d4d0..6289d74 100644
--- a/daemon/upcall.h
+++ b/daemon/upcall.h
@@ -67,8 +67,8 @@ typedef struct __readwrite_upcall_args {
 } readwrite_upcall_args;
 
 typedef struct __lock_upcall_args {
-    LONGLONG offset;
-    LONGLONG length;
+    uint64_t offset;
+    uint64_t length;
     BOOLEAN exclusive;
     BOOLEAN blocking;
 } lock_upcall_args;
diff --git a/sys/nfs41_driver.c b/sys/nfs41_driver.c
index 77bf814..4c2c73a 100644
--- a/sys/nfs41_driver.c
+++ b/sys/nfs41_driver.c
@@ -4404,6 +4404,11 @@ NTSTATUS nfs41_IsLockRealizable (
         ByteOffset->QuadPart,Length->QuadPart,
         BooleanFlagOn(LowIoLockFlags, SL_EXCLUSIVE_LOCK),
         !BooleanFlagOn(LowIoLockFlags, SL_FAIL_IMMEDIATELY));
+
+    /* NFS lock operations with length=0 MUST fail with NFS4ERR_INVAL */
+    if (Length->QuadPart == 0)
+        status = STATUS_NOT_SUPPORTED;
+
     DbgEx();
     return status;
 }