diff --git a/Makefile b/Makefile
index 987ee9b..995311f 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
 # Copyright (c) Infineon Technologies AG
 
 CC=gcc
-CFLAGS=-Wall -Wextra -g
+CFLAGS=-Wall -Wextra -std=c99 -g
 
 all: eltt2
 
diff --git a/eltt2.h b/eltt2.h
index e9ca42e..7cff7c0 100644
--- a/eltt2.h
+++ b/eltt2.h
@@ -67,8 +67,10 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <unistd.h>
+#include <getopt.h>
 #include <ctype.h>
 #include <string.h>
+#include <strings.h>
 
 //-------------"Defines"-------------
 #define TPM_RESP_MAX_SIZE		4096			///< This is the maximum possible TPM response size in bytes.