diff --git a/src/error.c b/src/error.c
index 4bda854..afb7af1 100644
--- a/src/error.c
+++ b/src/error.c
@@ -106,7 +106,7 @@
   X(WSASYSNOTREADY, ENETDOWN)                \
   X(WSAVERNOTSUPPORTED, ENOSYS)
 
-errno_t err_map_win_error_to_errno(DWORD error) {
+static errno_t _err_map_win_error_to_errno(DWORD error) {
   switch (error) {
 #define X(error_sym, errno_sym) \
   case error_sym:               \
@@ -122,7 +122,7 @@ void err_set_win_error(DWORD error) {
     error = GetLastError();
   else
     SetLastError(error);
-  errno = err_map_win_error_to_errno(error);
+  errno = _err_map_win_error_to_errno(error);
 }
 
 int err_check_handle(HANDLE handle) {
diff --git a/src/error.h b/src/error.h
index ea17c1b..dd1f290 100644
--- a/src/error.h
+++ b/src/error.h
@@ -12,7 +12,6 @@
 
 #define return_error(value, ...) _return_error_helper(__VA_ARGS__ + 0, value)
 
-WEPOLL_INTERNAL errno_t err_map_win_error_to_errno(DWORD error);
 WEPOLL_INTERNAL void err_set_win_error(DWORD error);
 WEPOLL_INTERNAL int err_check_handle(HANDLE handle);