diff --git a/libaegisub/common/util.cpp b/libaegisub/common/util.cpp
index 117696e424..de23eeabc3 100644
--- a/libaegisub/common/util.cpp
+++ b/libaegisub/common/util.cpp
@@ -186,6 +186,13 @@ void InitLocale() {
 	// FIXME: Should the ICU locale also be forced to en_US here?
 	if (result != std::codecvt_base::ok)
 		locale = boost::locale::generator().generate("en_US.UTF-8");
+
+	// Use the standard library's number parsing and formatting rather than
+	// Boost.Locale's, which nothing relies on. Boost.Locale's facets fall back
+	// to std::num_get code inlined from the SDK's libc++ headers, and with
+	// newer SDKs that code overflows a stack buffer when it calls into an
+	// older system libc++ (e.g. on macOS 13).
+	locale = std::locale(locale, std::locale::classic(), std::locale::numeric);
 	std::locale::global(locale);
 }
 } // namespace util
diff --git a/tests/tests/util.cpp b/tests/tests/util.cpp
index 14757f8bbd..afb3632395 100644
--- a/tests/tests/util.cpp
+++ b/tests/tests/util.cpp
@@ -18,6 +18,9 @@
 
 #include <main.h>
 
+#include <locale>
+#include <typeinfo>
+
 class lagi_util : public libagi { };
 
 namespace agi {
@@ -42,4 +45,11 @@ TEST(lagi_util, try_parse_int) {
 	EXPECT_EQ(1.0, i);
 }
 
+TEST(lagi_util, init_locale_uses_std_numeric_facets) {
+	// Boost.Locale's numeric facets crash on older macOS when built with a
+	// newer SDK (#733), so InitLocale must not install them
+	EXPECT_EQ(typeid(std::num_get<char>), typeid(std::use_facet<std::num_get<char>>(std::locale())));
+	EXPECT_EQ(typeid(std::num_put<char>), typeid(std::use_facet<std::num_put<char>>(std::locale())));
+}
+
 }