diff --git a/CMakeLists.txt b/CMakeLists.txt
index 43a00e68f19b..4f3cdb3fd987 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -288,6 +288,7 @@ if (FMT_MODULE)
 endif ()
 if (FMT_OS)
   target_sources(fmt PRIVATE src/os.cc)
+else()
   target_compile_definitions(fmt PRIVATE FMT_OS=0)
 endif ()
 
diff --git a/src/fmt.cc b/src/fmt.cc
index b3d344c61a77..6cff309d41c6 100644
--- a/src/fmt.cc
+++ b/src/fmt.cc
@@ -113,4 +113,4 @@ module :private;
 #include "format.cc"
 #if FMT_OS
 #  include "os.cc"
-#endif
\ No newline at end of file
+#endif