--- ./src/mongoc/mongoc-counters-private.h.ORIGIN	2018-04-23 17:53:12 +0200
+++ ./src/mongoc/mongoc-counters-private.h	2018-04-23 17:54:02 +0200
@@ -72,7 +72,7 @@
    }
 
    return len;
-#elif defined(__APPLE__) || defined(__sun)
+#elif defined(__APPLE__) || defined(__sun) || defined(_AIX)
    int ncpu;
 
    ncpu = (int) sysconf (_SC_NPROCESSORS_ONLN);