diff --git a/tools/cpu/nios2/ptf.c b/tools/cpu/nios2/ptf.c
index 076c287222..7a31c11632 100644
--- a/tools/cpu/nios2/ptf.c
+++ b/tools/cpu/nios2/ptf.c
@@ -10,6 +10,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <ctype.h>
 #include "ptf.h"
 
 #define PTFPARSER_MAXDEPTH 20