diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 00cf51cfc2e6..c7093bd9f2d3 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -28,6 +28,7 @@
 #include "bitops.h"
 #include <asm/cpufeature.h>
 #include <asm/processor-flags.h>
+#include "ctype.h"
 
 /* Useful macros */
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
@@ -200,8 +201,6 @@ static inline int memcmp_gs(const void *s1, addr_t s2, size_t len)
 	return diff;
 }
 
-#include "isdigit.h"
-
 /* Heap -- available for dynamic lists. */
 extern char _end[];
 extern char *HEAP;
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index a267849ac1c9..3f19c81a6203 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -20,6 +20,7 @@
 #include <asm/bootparam.h>
 
 #define BOOT_BOOT_H
+#include "../ctype.h"
 
 /* misc.c */
 extern struct boot_params *real_mode;		/* Pointer to real-mode data */
diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
index 7995c6a49509..19b3e693cd72 100644
--- a/arch/x86/boot/compressed/string.c
+++ b/arch/x86/boot/compressed/string.c
@@ -1,4 +1,2 @@
 #include "misc.h"
-
-#include "../isdigit.h"
 #include "../string.c"
diff --git a/arch/x86/boot/isdigit.h b/arch/x86/boot/ctype.h
similarity index 100%
rename from arch/x86/boot/isdigit.h
rename to arch/x86/boot/ctype.h