diff --git a/lib/src/lib.c b/lib/src/lib.c
index 104ded78..fc5fbc92 100644
--- a/lib/src/lib.c
+++ b/lib/src/lib.c
@@ -4,7 +4,7 @@
 //   - include
 //   - utf8proc
 
-#define _POSIX_SOURCE
+#define _POSIX_C_SOURCE 200112L
 #define UTF8PROC_STATIC
 
 #include "./get_changed_ranges.c"