diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index e5ab51f..99747a5 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1496,13 +1496,14 @@
 		case FORMAT_TYPE_STR: {
 			const char *save_str = va_arg(args, char *);
 			size_t len;
+
 			if ((unsigned long)save_str > (unsigned long)-PAGE_SIZE
 					|| (unsigned long)save_str < PAGE_SIZE)
 				save_str = "(null)";
-			len = strlen(save_str);
-			if (str + len + 1 < end)
-				memcpy(str, save_str, len + 1);
-			str += len + 1;
+			len = strlen(save_str) + 1;
+			if (str + len < end)
+				memcpy(str, save_str, len);
+			str += len;
 			break;
 		}