diff --git a/include/fmt/os.h b/include/fmt/os.h
index 38664950..2a7ebead 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -382,7 +382,9 @@ struct ostream_params {
 class ostream_buffer final : public detail::buffer<char> {
   file file_;
 
-  FMT_API void grow(size_t) override;
+  void grow(size_t) override {
+    if (this->size() == this->capacity()) flush();
+  }
 
  public:
   ostream_buffer(cstring_view path, const detail::ostream_params& params)
diff --git a/src/os.cc b/src/os.cc
index c40fdaea..06f400df 100644
--- a/src/os.cc
+++ b/src/os.cc
@@ -366,10 +366,6 @@ long getpagesize() {
 #  endif
 }
 
-FMT_API void detail::ostream_buffer::grow(size_t) {
-  if (this->size() == this->capacity()) flush();
-}
-
 ostream::~ostream() = default;
 #endif  // FMT_USE_FCNTL
 FMT_END_NAMESPACE