diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index e5caadd..9c0e556 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -74,9 +74,9 @@
     return (float)strtod(nptr, endptr);
 }
 
-extern int atoi(const char *);
-extern long atol(const char *);
-extern long long atoll(const char *);
+extern int atoi(const char *) __purefunc;
+extern long atol(const char *) __purefunc;
+extern long long atoll(const char *) __purefunc;
 
 static __inline__ double atof(const char *nptr)
 {