diff --git a/ncrystal_core/src/NCFileUtilsWin.cc b/ncrystal_core/src/NCFileUtilsWin.cc
index daafc8df..92775184 100644
--- a/ncrystal_core/src/NCFileUtilsWin.cc
+++ b/ncrystal_core/src/NCFileUtilsWin.cc
@@ -34,7 +34,7 @@
 
 //Do not use std::filesystem if we have an alternative:
 #ifndef NCRYSTAL_AVOID_CPP17FILESYSTEM
-#  if NCRYSTAL_FEATURE_IFSTREAM_WSTRING_PATH
+#  ifdef NCRYSTAL_FEATURE_IFSTREAM_WSTRING_PATH
 #    define NCRYSTAL_AVOID_CPP17FILESYSTEM
 #  endif
 #endif