diff --git a/zipl/boot/ebcdic.c b/zipl/boot/ebcdic.c
index be3441b7..2d0bb536 100644
--- a/zipl/boot/ebcdic.c
+++ b/zipl/boot/ebcdic.c
@@ -8,11 +8,13 @@
  *
  */
 
+#include <limits.h>
+
 #include "ebcdic.h"
 
-
 /*
- * Convert ebcdic string to number with given base
+ * Convert EBCDIC string to number with given base. In case of an overflow,
+ * ULONG_MAX is returned and @endptr is not updated.
  */
 unsigned long ebcdic_strtoul(char *nptr, char **endptr, int base)
 {
@@ -21,7 +23,8 @@ unsigned long ebcdic_strtoul(char *nptr, char **endptr, int base)
 	while (ebcdic_isdigit(*nptr)) {
 		if (val != 0)
 			val *= base;
-		val += *nptr - 0xf0;
+		if (__builtin_uaddl_overflow(val, *nptr - 0xf0, &val))
+			return ULONG_MAX;
 		nptr++;
 	}
 	if (endptr)
diff --git a/zipl/boot/menu.c b/zipl/boot/menu.c
index 6d30cf81..73bb11d2 100644
--- a/zipl/boot/menu.c
+++ b/zipl/boot/menu.c
@@ -27,12 +27,12 @@ static void menu_prompt(int timeout)
 		printf("Please choose:");
 }
 
-static int menu_read(void)
+static unsigned long menu_read(void)
 {
 	char *temp_area =  (char *)get_zeroed_page();
 	int timeout, rc, i, count = 0;
+	unsigned long value;
 	char *endptr;
-	int value;
 
 	timeout = __stage2_params.timeout;