diff --git a/src/fallback.cpp b/src/fallback.cpp
index 722338c04..64bbc1920 100644
--- a/src/fallback.cpp
+++ b/src/fallback.cpp
@@ -397,6 +397,7 @@ int flock(int fd, int op) {
 
 #if !defined(HAVE_WCSTOD_L) && !defined(__NetBSD__)
 #undef wcstod_l
+#include <locale.h>
 // For platforms without wcstod_l C extension, wrap wcstod after changing the
 // thread-specific locale.
 double fish_compat::wcstod_l(const wchar_t *enptr, wchar_t **endptr, locale_t loc) {