--- a/targets/Linux/plc_Linux_main.c	Mon Jan 15 14:43:53 2018 +0100
+++ b/targets/Linux/plc_Linux_main.c	Fri Jan 19 15:12:23 2018 +0100
@@ -232,6 +232,7 @@
     pthread_mutex_lock(&python_mutex);
 }
 
+#ifndef HAVE_RETAIN
 void InitRetain(void)
 {
 }
@@ -260,3 +261,4 @@
 void Remind(unsigned int offset, unsigned int count, void *p)
 {
 }
+#endif // !HAVE_RETAIN

--- a/targets/Win32/plc_Win32_main.c	Mon Jan 15 14:43:53 2018 +0100
+++ b/targets/Win32/plc_Win32_main.c	Fri Jan 19 15:12:23 2018 +0100
@@ -241,6 +241,7 @@
 	WaitForSingleObject(python_sem, INFINITE);
 }
 
+#ifndef HAVE_RETAIN
 void InitRetain(void)
 {
 }
@@ -275,6 +276,7 @@
 void Remind(unsigned int offset, unsigned int count, void *p)
 {
 }
+#endif // !HAVE_RETAIN
 
 static void __attribute__((constructor))
 beremiz_dll_init(void)

--- a/targets/Xenomai/plc_Xenomai_main.c	Mon Jan 15 14:43:53 2018 +0100
+++ b/targets/Xenomai/plc_Xenomai_main.c	Fri Jan 19 15:12:23 2018 +0100
@@ -363,6 +363,7 @@
     }    /* as plc does not wait for lock. */
 }
 
+#ifndef HAVE_RETAIN
 int CheckRetainBuffer(void)
 {
 	return 1;
@@ -391,3 +392,4 @@
 void InitRetain(void)
 {
 }
+#endif // !HAVE_RETAIN

--- a/targets/Xenomai/plc_Xenomai_noretain.c	Mon Jan 15 14:43:53 2018 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,28 +0,0 @@
-int CheckRetainBuffer(void)
-{
-	return 1;
-}
-
-void ValidateRetainBuffer(void)
-{
-}
-
-void InValidateRetainBuffer(void)
-{
-}
-
-void Retain(unsigned int offset, unsigned int count, void *p)
-{
-}
-
-void Remind(unsigned int offset, unsigned int count, void *p)
-{
-}
-
-void CleanupRetain(void)
-{
-}
-
-void InitRetain(void)
-{
-}