diff --git a/compiler/pathutils.nim b/compiler/pathutils.nim
index 8138a245ac..3a501a417b 100644
--- a/compiler/pathutils.nim
+++ b/compiler/pathutils.nim
@@ -12,7 +12,7 @@
 
 import os, pathnorm
 
-when defined(nimSlimSystem):
+when defined(nimPreviewSlimSystem):
   import std/syncio
 
 type
diff --git a/lib/posix/posix.nim b/lib/posix/posix.nim
index c10fc6ac92..9c65d07329 100644
--- a/lib/posix/posix.nim
+++ b/lib/posix/posix.nim
@@ -37,7 +37,7 @@
 when defined(nimHasStyleChecks):
   {.push styleChecks: off.}
 
-when defined(nimSlimSystem):
+when defined(nimPreviewSlimSystem):
   import std/syncio
 
 # TODO these constants don't seem to be fetched from a header file for unknown
diff --git a/tests/test_nimscript.nims b/tests/test_nimscript.nims
index b380570ffa..5fc77f6e4b 100644
--- a/tests/test_nimscript.nims
+++ b/tests/test_nimscript.nims
@@ -5,7 +5,7 @@
 
 from stdtest/specialpaths import buildDir
 
-when defined(nimSlimSystem):
+when defined(nimPreviewSlimSystem):
   import std/syncio
 
 import std/[