Index: bctoolbox-5.1.17/src/utils/port.c
===================================================================
--- bctoolbox-5.1.17.orig/src/utils/port.c
+++ bctoolbox-5.1.17/src/utils/port.c
@@ -398,6 +398,7 @@ char * WSAAPI gai_strerror(int errnum){
 #include <netdb.h>
 #include <sys/un.h>
 #include <sys/stat.h>
+#include <stddef.h>
 
 static char *make_pipe_name(const char *name){
 	return bctbx_strdup_printf("/tmp/%s",name);
@@ -1508,6 +1509,7 @@ char * bctbx_concat(const char *str, ...
 			/* Resize the allocated memory if necessary.  */
 			if (wp + len + 1 > result + allocated)
 			{
+				ptrdiff_t offset = wp - result;
 				allocated = (allocated + len) * 2;
 				newp = (char *) realloc (result, allocated);
 				if (newp == NULL)
@@ -1515,7 +1517,7 @@ char * bctbx_concat(const char *str, ...
 					free (result);
 					return NULL;
 				}
-				wp = newp + (wp - result);
+				wp = newp + offset;
 				result = newp;
 			}
 			memcpy (wp, s, len);