1 files changed, 3 insertions, 0 deletions

diff --git a/lib/pure/lexbase.nim b/lib/pure/lexbase.nim
index bbc0a38ae..336a57ec1 100644
--- a/lib/pure/lexbase.nim
+++ b/lib/pure/lexbase.nim
@@ -14,6 +14,9 @@
 import
   strutils, streams
 
+when defined(nimPreviewSlimSystem):
+  import std/assertions
+
 const
   EndOfFile* = '\0' ## end of file marker
   NewLines* = {'\c', '\L'}