diff --git a/include/spdlog/details/os-inl.h b/include/spdlog/details/os-inl.h
index aa4ff709..4c17804b 100644
--- a/include/spdlog/details/os-inl.h
+++ b/include/spdlog/details/os-inl.h
@@ -33,6 +33,7 @@
 
 #    if defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) || defined(SPDLOG_WCHAR_FILENAMES)
 #        include <limits>
+#        include <spdlog/details/fmt_helper.h>
 #    endif
 
 #    include <direct.h> // for _mkdir/_wmkdir
diff --git a/tests/includes.h b/tests/includes.h
index 7285873a..e6805280 100644
--- a/tests/includes.h
+++ b/tests/includes.h
@@ -17,6 +17,7 @@
 
 #include "spdlog/spdlog.h"
 #include "spdlog/async.h"
+#include "spdlog/details/fmt_helper.h"
 #include "spdlog/sinks/basic_file_sink.h"
 #include "spdlog/sinks/daily_file_sink.h"
 #include "spdlog/sinks/null_sink.h"
diff --git a/tests/test_fmt_helper.cpp b/tests/test_fmt_helper.cpp
index a7edccf3..a9db5d02 100644
--- a/tests/test_fmt_helper.cpp
+++ b/tests/test_fmt_helper.cpp
@@ -1,6 +1,5 @@
 
 #include "includes.h"
-#include "spdlog/details/fmt_helper.h"
 
 using spdlog::memory_buf_t;
 using spdlog::details::fmt_helper::to_string_view;