diff --git a/src/system/libroot/add-ons/icu/ICULocaleBackend.cpp b/src/system/libroot/add-ons/icu/ICULocaleBackend.cpp
index 7c9657a496..44986a0c83 100644
--- a/src/system/libroot/add-ons/icu/ICULocaleBackend.cpp
+++ b/src/system/libroot/add-ons/icu/ICULocaleBackend.cpp
@@ -88,6 +88,13 @@ ICULocaleBackend::SetLocale(int category, const char* posixLocaleName)
 		return _SetPosixLocale(category);
 
 	Locale locale = Locale::createCanonical(posixLocaleName);
+
+	// Locale::create doesn't check validity, so make sure the locale
+	// has a real ISO-3166 language code to validate that it actually exists.
+	const char* iso3166 = locale.getISO3Language();
+	if (iso3166 == NULL || iso3166[0] == '\0')
+		return NULL;
+
 	switch (category) {
 		case LC_ALL:
 			if (fCollateData.SetTo(locale, posixLocaleName) != B_OK