diff --git a/libc/include/time.h b/libc/include/time.h
index 691aa06..898b816 100644
--- a/libc/include/time.h
+++ b/libc/include/time.h
@@ -76,7 +76,12 @@
 
 char* strptime(const char*, const char*, struct tm*);
 size_t strftime(char*, size_t, const char*, const struct tm*);
+
+#if __ANDROID_API__ >= 21
 size_t strftime_l(char*, size_t, const char*, const struct tm*, locale_t) __INTRODUCED_IN(21);
+#else
+// Implemented as static inline before 21.
+#endif
 
 char* ctime(const time_t*);
 char* ctime_r(const time_t*, char*);