diff --git a/src/core/debug.c b/src/core/debug.c
index 627d5d9a1..2161f9731 100644
--- a/src/core/debug.c
+++ b/src/core/debug.c
@@ -22,6 +22,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <stdio.h>
 #include <stdint.h>
 #include <stdarg.h>
+#include <ctype.h>
 #include <ipxe/console.h>
 
 /**
@@ -96,9 +97,7 @@ static void dbg_hex_dump_da_row ( unsigned long dispaddr, const void *data,
 			continue;
 		}
 		byte = bytes[i];
-		if ( ( byte < 0x20 ) || ( byte >= 0x7f ) )
-			byte = '.';
-		dbg_printf ( "%c", byte );
+		dbg_printf ( "%c", ( isprint ( byte ) ? byte : '.' ) );
 	}
 	dbg_printf ( "\n" );
 }
diff --git a/src/include/ctype.h b/src/include/ctype.h
index 9f5127bf1..e92ecb1c0 100644
--- a/src/include/ctype.h
+++ b/src/include/ctype.h
@@ -12,6 +12,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define islower(c)	((c) >= 'a' && (c) <= 'z')
 #define isupper(c)	((c) >= 'A' && (c) <= 'Z')
 #define isxdigit(c)	(isdigit(c) || ((c) >= 'A' && (c) <= 'F') || ((c) >= 'a' && (c) <= 'f'))
+#define isprint(c)	((c) >= ' ' && (c) <= '~' )
 
 static inline unsigned char tolower(unsigned char c)
 {