diff -up c2esp-27/src/c2espC.c.ftbfs-gcc7 c2esp-27/src/c2espC.c
diff -up c2esp-27/src/c2espcommon.c.ftbfs-gcc7 c2esp-27/src/c2espcommon.c
--- c2esp-27/src/c2espcommon.c.ftbfs-gcc7	2017-03-03 14:10:28.018395128 +0100
+++ c2esp-27/src/c2espcommon.c	2017-03-03 14:19:26.967383931 +0100
@@ -24,6 +24,7 @@
 #include <fcntl.h> //files
 #include <sys/stat.h> //for chmod
 #include <time.h> //time functions used for debugging
+#include <stdlib.h>
 
 #if HAVE_CUPSFILTERS_DRIVER_H == 1
 #include <cupsfilters/driver.h> //has the dither functions
diff -up c2esp-27/src/c2espcommon.h.ftbfs-gcc7 c2esp-27/src/c2espcommon.h
--- c2esp-27/src/c2espcommon.h.ftbfs-gcc7	2017-03-03 14:25:54.186413550 +0100
+++ c2esp-27/src/c2espcommon.h	2017-03-03 14:26:53.105961575 +0100
@@ -21,6 +21,7 @@
 #include <cups/sidechannel.h> //FlushBackChannel, and the side channel functions and constants
 #include <fcntl.h> //files
 #include <time.h> //time functions used for debugging
+#include <stdio.h> //library for stderr, stdout, stdin - because of gcc7, it needed to be included
 
 /*
  * Constants...