diff --git a/dlls/kernel/sync.c b/dlls/kernel/sync.c
index bada447e979..fd0b9eaa8b9 100644
--- a/dlls/kernel/sync.c
+++ b/dlls/kernel/sync.c
@@ -1672,7 +1672,10 @@ HANDLE WINAPI CreateMailslotW( LPCWSTR lpName, DWORD nMaxMessageSize,
     attr.SecurityDescriptor = sa ? sa->lpSecurityDescriptor : NULL;
     attr.SecurityQualityOfService = NULL;
 
-    timeout.QuadPart = (ULONGLONG) lReadTimeout * -10000;
+    if (lReadTimeout != MAILSLOT_WAIT_FOREVER)
+        timeout.QuadPart = (ULONGLONG) lReadTimeout * -10000;
+    else
+        timeout.QuadPart = ((LONGLONG)0x7fffffff << 32) | 0xffffffff;
 
     status = NtCreateMailslotFile( &handle, GENERIC_READ | GENERIC_WRITE, &attr,
                                    &iosb, 0, 0, nMaxMessageSize, &timeout );
diff --git a/dlls/ntdll/file.c b/dlls/ntdll/file.c
index 13105291591..b5d3f6ab1aa 100644
--- a/dlls/ntdll/file.c
+++ b/dlls/ntdll/file.c
@@ -2061,7 +2061,7 @@ NTSTATUS WINAPI NtCreateMailslotFile(PHANDLE pHandle, ULONG DesiredAccess,
         req->access = DesiredAccess;
         req->attributes = (attr) ? attr->Attributes : 0;
         req->max_msgsize = MaxMessageSize;
-        req->read_timeout = TimeOut->QuadPart / -10000;
+        req->read_timeout = (TimeOut->QuadPart <= 0) ? TimeOut->QuadPart / -10000 : -1;
         wine_server_add_data( req, attr->ObjectName->Buffer + 4,
                               attr->ObjectName->Length - 4*sizeof(WCHAR) );
         ret = wine_server_call( req );
diff --git a/include/wine/server_protocol.h b/include/wine/server_protocol.h
index e8dc3b346cb..168e9316727 100644
--- a/include/wine/server_protocol.h
+++ b/include/wine/server_protocol.h
@@ -3532,7 +3532,7 @@ struct create_mailslot_request
     unsigned int   access;
     unsigned int   attributes;
     unsigned int   max_msgsize;
-    unsigned int   read_timeout;
+    int            read_timeout;
     /* VARARG(name,unicode_str); */
 };
 struct create_mailslot_reply
@@ -3564,13 +3564,13 @@ struct set_mailslot_info_request
     struct request_header __header;
     obj_handle_t   handle;
     unsigned int   flags;
-    unsigned int   read_timeout;
+    int            read_timeout;
 };
 struct set_mailslot_info_reply
 {
     struct reply_header __header;
     unsigned int   max_msgsize;
-    unsigned int   read_timeout;
+    int            read_timeout;
     unsigned int   msg_count;
     unsigned int   next_msgsize;
 };
@@ -4208,6 +4208,6 @@ union generic_reply
     struct set_mailslot_info_reply set_mailslot_info_reply;
 };
 
-#define SERVER_PROTOCOL_VERSION 198
+#define SERVER_PROTOCOL_VERSION 199
 
 #endif /* __WINE_WINE_SERVER_PROTOCOL_H */
diff --git a/server/mailslot.c b/server/mailslot.c
index 918bcdda761..d421a9d2942 100644
--- a/server/mailslot.c
+++ b/server/mailslot.c
@@ -56,7 +56,7 @@ struct mailslot
     struct fd          *fd;
     struct fd          *write_fd;
     unsigned int        max_msgsize;
-    unsigned int        read_timeout;
+    int                 read_timeout;
     struct list         writers;
 };
 
@@ -207,8 +207,7 @@ static void mailslot_queue_async( struct fd *fd, void *apc, void *user,
         return;
     }
 
-    if (mailslot->read_timeout != MAILSLOT_WAIT_FOREVER)
-        timeout = &mailslot->read_timeout;
+    if (mailslot->read_timeout != -1) timeout = &mailslot->read_timeout;
 
     fd_queue_async_timeout( fd, apc, user, iosb, type, count, timeout );
 }
diff --git a/server/protocol.def b/server/protocol.def
index 23140dfe4a5..95ec43b5433 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -2475,7 +2475,7 @@ enum message_type
     unsigned int   access;        /* wanted access rights */
     unsigned int   attributes;    /* object attributes */
     unsigned int   max_msgsize;
-    unsigned int   read_timeout;
+    int            read_timeout;
     VARARG(name,unicode_str);     /* mailslot name */
 @REPLY
     obj_handle_t   handle;        /* handle to the mailslot */
@@ -2497,10 +2497,10 @@ enum message_type
 @REQ(set_mailslot_info)
     obj_handle_t   handle;        /* handle to the mailslot */
     unsigned int   flags;
-    unsigned int   read_timeout;
+    int            read_timeout;
 @REPLY
     unsigned int   max_msgsize;
-    unsigned int   read_timeout;
+    int            read_timeout;
     unsigned int   msg_count;
     unsigned int   next_msgsize;
 @END
diff --git a/server/trace.c b/server/trace.c
index 7f98962662c..d3899978e48 100644
--- a/server/trace.c
+++ b/server/trace.c
@@ -3052,7 +3052,7 @@ static void dump_create_mailslot_request( const struct create_mailslot_request *
     fprintf( stderr, " access=%08x,", req->access );
     fprintf( stderr, " attributes=%08x,", req->attributes );
     fprintf( stderr, " max_msgsize=%08x,", req->max_msgsize );
-    fprintf( stderr, " read_timeout=%08x,", req->read_timeout );
+    fprintf( stderr, " read_timeout=%d,", req->read_timeout );
     fprintf( stderr, " name=" );
     dump_varargs_unicode_str( cur_size );
 }
@@ -3080,13 +3080,13 @@ static void dump_set_mailslot_info_request( const struct set_mailslot_info_reque
 {
     fprintf( stderr, " handle=%p,", req->handle );
     fprintf( stderr, " flags=%08x,", req->flags );
-    fprintf( stderr, " read_timeout=%08x", req->read_timeout );
+    fprintf( stderr, " read_timeout=%d", req->read_timeout );
 }
 
 static void dump_set_mailslot_info_reply( const struct set_mailslot_info_reply *req )
 {
     fprintf( stderr, " max_msgsize=%08x,", req->max_msgsize );
-    fprintf( stderr, " read_timeout=%08x,", req->read_timeout );
+    fprintf( stderr, " read_timeout=%d,", req->read_timeout );
     fprintf( stderr, " msg_count=%08x,", req->msg_count );
     fprintf( stderr, " next_msgsize=%08x", req->next_msgsize );
 }