diff --git a/lib/system/sysstr.nim b/lib/system/sysstr.nim
index eb3d276e0..3e170172b 100644
--- a/lib/system/sysstr.nim
+++ b/lib/system/sysstr.nim
@@ -292,7 +292,7 @@ proc nimFloatToStr(f: float): string {.compilerproc.} =
     buf[n+2] = '\0'
   # On Windows nice numbers like '1.#INF', '-1.#INF' or '1.#NAN' are produced.
   # We want to get rid of these here:
-  if buf[n-1] == 'N':
+  if buf[n-1] in {'n', 'N'}:
     result = "nan"
   elif buf[n-1] == 'F':
     if buf[0] == '-':