diff --git a/rtl/wasi/sysfile.inc b/rtl/wasi/sysfile.inc
index 8cb5fea437..99d25cf4b1 100644
--- a/rtl/wasi/sysfile.inc
+++ b/rtl/wasi/sysfile.inc
@@ -100,6 +100,99 @@ begin
 end;
 
 procedure Do_Open(var f; p: pchar; flags: longint; pchangeable: boolean);
-begin
-  DebugWriteLn('Do_Open');
+{
+  FileRec and textrec have both Handle and mode as the first items so
+  they could use the same routine for opening/creating.
+  when (flags and $100)   the file will be append
+  when (flags and $1000)  the file will be truncate/rewritten
+  when (flags and $10000) there is no check for close (needed for textfiles)
+}
+var
+  oflags : __wasi_oflags_t = 0;
+  fs_rights_base: __wasi_rights_t = 0;
+  fdflags: __wasi_fdflags_t = 0;
+  ourfd: __wasi_fd_t;
+  res: __wasi_errno_t;
+Begin
+{ close first if opened }
+  if ((flags and $10000)=0) then
+   begin
+     case FileRec(f).mode of
+      fminput,fmoutput,fminout : Do_Close(FileRec(f).Handle);
+      fmclosed : ;
+     else
+      begin
+        inoutres:=102; {not assigned}
+        exit;
+      end;
+     end;
+   end;
+{ reset file Handle }
+  FileRec(f).Handle:=UnusedHandle;
+{ We do the conversion of filemodes here, concentrated on 1 place }
+  case (flags and 3) of
+   0 : begin
+         fs_rights_base :=__WASI_RIGHTS_FD_READ;
+         FileRec(f).mode:=fminput;
+       end;
+   1 : begin
+         fs_rights_base :=__WASI_RIGHTS_FD_WRITE;
+         FileRec(f).mode:=fmoutput;
+       end;
+   2 : begin
+         fs_rights_base :=__WASI_RIGHTS_FD_READ or __WASI_RIGHTS_FD_WRITE;
+         FileRec(f).mode:=fminout;
+       end;
+  end;
+  if (flags and $1000)=$1000 then
+   oflags:=oflags or (__WASI_OFLAGS_CREAT or __WASI_OFLAGS_TRUNC)
+  else
+   if (flags and $100)=$100 then
+    fdflags:=fdflags or __WASI_FDFLAGS_APPEND;
+{ empty name is special }
+  if p[0]=#0 then
+   begin
+     case FileRec(f).mode of
+       fminput :
+         FileRec(f).Handle:=StdInputHandle;
+       fminout, { this is set by rewrite }
+       fmoutput :
+         FileRec(f).Handle:=StdOutputHandle;
+       fmappend :
+         begin
+           FileRec(f).Handle:=StdOutputHandle;
+           FileRec(f).mode:=fmoutput; {fool fmappend}
+         end;
+     end;
+     exit;
+   end;
+{ real open call }
+  repeat
+    res:=path_open(0,
+                   0,
+                   p,
+                   strlen(p),
+                   oflags,
+                   fs_rights_base,
+                   fs_rights_base,
+                   fdflags,
+                   @ourfd);
+  until (res=__WASI_ERRNO_SUCCESS) or (res<>__WASI_ERRNO_INTR);
+  {if (res=__WASI_ERRNO_ROFS) and ((OFlags and O_RDWR)<>0) then
+   begin
+     Oflags:=Oflags and not(O_RDWR);
+     repeat
+       FileRec(f).Handle:=Fpopen(p,oflags,MODE_OPEN);
+     until (FileRec(f).Handle<>-1) or (geterrno<>ESysEINTR);
+   end;}
+  If res<>__WASI_ERRNO_SUCCESS Then
+    begin
+      FileRec(f).mode:=fmclosed;
+      InOutRes:=Errno2InoutRes(res);
+    end
+  else
+    begin
+      FileRec(f).Handle:=ourfd;
+      InOutRes:=0;
+    end;
 end;
diff --git a/rtl/wasi/system.pp b/rtl/wasi/system.pp
index ef1749a3cf..2c3c66b449 100644
--- a/rtl/wasi/system.pp
+++ b/rtl/wasi/system.pp
@@ -46,6 +46,7 @@ implementation
 type
   P__wasi_size_t = ^__wasi_size_t;
   __wasi_size_t = longint;
+  P__wasi_fd_t = ^__wasi_fd_t;
   __wasi_fd_t = longint;
   size_t = longint;
   __wasi_errno_t = longint;
@@ -209,6 +210,20 @@ type
     fs_rights_inheriting: __wasi_rights_t;
   end;
 
+  __wasi_lookupflags_t = UInt32;
+
+const
+  __WASI_LOOKUPFLAGS_SYMLINK_FOLLOW = 1;
+
+type
+  __wasi_oflags_t = UInt16;
+
+const
+  __WASI_OFLAGS_CREAT     = 1;
+  __WASI_OFLAGS_DIRECTORY = 2;
+  __WASI_OFLAGS_EXCL      = 4;
+  __WASI_OFLAGS_TRUNC     = 8;
+
 function fd_write(fd: __wasi_fd_t;
                   iovs: P__wasi_ciovec_t;
                   iovs_len: size_t;
@@ -220,6 +235,15 @@ function fd_read(fd: __wasi_fd_t;
 procedure proc_exit(rval: __wasi_exitcode_t); noreturn; external 'wasi_snapshot_preview1';
 function fd_fdstat_get(fd: __wasi_fd_t;
                        stat: P__wasi_fdstat_t): __wasi_errno_t; external 'wasi_snapshot_preview1';
+function path_open(fd: __wasi_fd_t;
+                   dirflags: __wasi_lookupflags_t;
+                   path: PChar;
+                   path_len: size_t;
+                   oflags: __wasi_oflags_t;
+                   fs_rights_base,
+                   fs_rights_inherting: __wasi_rights_t;
+                   fdflags: __wasi_fdflags_t;
+                   opened_fd: P__wasi_fd_t): __wasi_errno_t; external 'wasi_snapshot_preview1';
 
 {$I system.inc}