diff --git a/plugins/api/api/c/posix.h b/plugins/api/api/c/posix.h
index 3744f1aae..19bf06f87 100644
--- a/plugins/api/api/c/posix.h
+++ b/plugins/api/api/c/posix.h
@@ -445,3 +445,6 @@ int isxdigit(int c);
 
 int isascii(int c);
 int isblank(int c);
+
+int toupper(int c);
+int tolower(int c);