diff --git a/lib/posix/posix.nim b/lib/posix/posix.nim
index 15ce82eb32176..4f9a311954b5c 100644
--- a/lib/posix/posix.nim
+++ b/lib/posix/posix.nim
@@ -37,8 +37,7 @@
 when defined(nimHasStyleChecks):
   {.push styleChecks: off.}
 
-when defined(nimPreviewSlimSystem):
-  import std/syncio
+from system/ansi_c import CFilePtr
 
 # TODO these constants don't seem to be fetched from a header file for unknown
 #      platforms - where do they come from and why are they here?
@@ -576,9 +575,9 @@ proc nice*(a1: cint): cint {.importc, header: "<unistd.h>".}
 proc pathconf*(a1: cstring, a2: cint): int {.importc, header: "<unistd.h>".}
 
 proc pause*(): cint {.importc, header: "<unistd.h>".}
-proc pclose*(a: File): cint {.importc, header: "<stdio.h>".}
+proc pclose*(a: CFilePtr): cint {.importc, header: "<stdio.h>".}
 proc pipe*(a: array[0..1, cint]): cint {.importc, header: "<unistd.h>".}
-proc popen*(a1, a2: cstring): File {.importc, header: "<stdio.h>".}
+proc popen*(a1, a2: cstring): CFilePtr {.importc, header: "<stdio.h>".}
 proc pread*(a1: cint, a2: pointer, a3: int, a4: Off): int {.
   importc, header: "<unistd.h>".}
 proc pwrite*(a1: cint, a2: pointer, a3: int, a4: Off): int {.
@@ -586,7 +585,7 @@ proc pwrite*(a1: cint, a2: pointer, a3: int, a4: Off): int {.
 proc read*(a1: cint, a2: pointer, a3: int): int {.importc, header: "<unistd.h>".}
 when not defined(nintendoswitch):
   proc readlink*(a1, a2: cstring, a3: int): int {.importc, header: "<unistd.h>".}
-proc ioctl*(f: FileHandle, device: uint): int {.importc: "ioctl",
+proc ioctl*(f: cint, device: uint): int {.importc: "ioctl",
       header: "<sys/ioctl.h>", varargs, tags: [WriteIOEffect].}
   ## A system call for device-specific input/output operations and other
   ## operations which cannot be expressed by regular system calls
diff --git a/lib/std/syncio.nim b/lib/std/syncio.nim
index 911bff276e173..1a0e27c0bc08b 100644
--- a/lib/std/syncio.nim
+++ b/lib/std/syncio.nim
@@ -18,10 +18,10 @@ when defined(windows):
 from system/ansi_c import c_memchr
 
 # ----------------- IO Part ------------------------------------------------
+from system/ansi_c import CFilePtr
+
 type
-  CFile {.importc: "FILE", header: "<stdio.h>",
-          incompleteStruct.} = object
-  File* = ptr CFile ## The type representing a file handle.
+  File* = CFilePtr ## The type representing a file handle.
 
   FileMode* = enum       ## The file mode when opening a file.
     fmRead,              ## Open the file for read access only.
@@ -293,13 +293,7 @@ when SupportIoctlInheritCtl:
   proc c_ioctl(fd: cint, request: cint): cint {.
     importc: "ioctl", header: "<sys/ioctl.h>", varargs.}
 elif defined(posix) and not defined(lwip) and not defined(nimscript):
-  var
-    F_GETFD {.importc, header: "<fcntl.h>".}: cint
-    F_SETFD {.importc, header: "<fcntl.h>".}: cint
-    FD_CLOEXEC {.importc, header: "<fcntl.h>".}: cint
-
-  proc c_fcntl(fd: cint, cmd: cint): cint {.
-    importc: "fcntl", header: "<fcntl.h>", varargs.}
+  from posix import F_GETFD, F_SETFD, FD_CLOEXEC, fcntl
 elif defined(windows):
   type
     WinDWORD = culong
@@ -384,11 +378,11 @@ when defined(nimdoc) or (defined(posix) and not defined(nimscript)) or defined(w
     elif defined(freertos) or defined(zephyr):
       result = true
     elif defined(posix):
-      var flags = c_fcntl(f, F_GETFD)
+      var flags = fcntl(f, F_GETFD)
       if flags == -1:
         return false
       flags = if inheritable: flags and not FD_CLOEXEC else: flags or FD_CLOEXEC
-      result = c_fcntl(f, F_SETFD, flags) != -1
+      result = fcntl(f, F_SETFD, flags) != -1
     else:
       result = setHandleInformation(cast[IoHandle](f), HANDLE_FLAG_INHERIT,
                                     inheritable.WinDWORD) != 0
@@ -676,35 +670,10 @@ const
     # should not be translated.
 
 when defined(posix) and not defined(nimscript):
-  when defined(linux) and defined(amd64):
-    type
-      Mode {.importc: "mode_t", header: "<sys/types.h>".} = cint
-
-      # fillers ensure correct size & offsets
-      Stat {.importc: "struct stat",
-              header: "<sys/stat.h>", final, pure.} = object ## struct stat
-        filler_1: array[24, char]
-        st_mode: Mode ## Mode of file
-        filler_2: array[144 - 24 - 4, char]
-
-    proc modeIsDir(m: Mode): bool =
-      ## Test for a directory.
-      (m and 0o170000) == 0o40000
-
-  else:
-    type
-      Mode {.importc: "mode_t", header: "<sys/types.h>".} = cint
-
-      Stat {.importc: "struct stat",
-               header: "<sys/stat.h>", final, pure.} = object ## struct stat
-        st_mode: Mode ## Mode of file
-
-    proc modeIsDir(m: Mode): bool {.importc: "S_ISDIR", header: "<sys/stat.h>".}
-      ## Test for a directory.
-
-  proc c_fstat(a1: cint, a2: var Stat): cint {.
-    importc: "fstat", header: "<sys/stat.h>".}
+  from posix import Mode, Stat, S_ISDIR, fstat
 
+  proc modeIsDir(m: Mode): bool =
+    S_ISDIR(m)
 
 proc open*(f: var File, filename: string,
           mode: FileMode = fmRead,
@@ -723,7 +692,7 @@ proc open*(f: var File, filename: string,
       # POSIX. We do not want to handle directories as regular files that can
       # be opened.
       var res {.noinit.}: Stat
-      if c_fstat(getFileHandle(f2), res) >= 0'i32 and modeIsDir(res.st_mode):
+      if fstat(getFileHandle(f2), res) >= 0'i32 and modeIsDir(res.st_mode):
         closeIgnoreError(f2)
         return false
     when not defined(nimInheritHandles) and declared(setInheritable) and