--- a/makelib/config-linux-gnu.make	Thu Jun 21 08:07:41 2018 +0000
+++ b/makelib/config-linux-gnu.make	Wed Jun 27 07:31:28 2018 +0000
@@ -15,8 +15,14 @@
 
 # We need to use at most GCC 6.x, some code may fail to compile
 # with GCC 7 due to -Werror (`send.c` for instance). We won't fix
-# that for Smalltalk/X 6.x.x, will be fixed only for Smalltalk/X 8.0.0
-ifeq ($(CC),cc)
+# that for Smalltalk/X 6.x.x, will be fixed only for Smalltalk/X 8.1.x 
+# series. 
+# 
+# Note, that we have to use the trick with `ifeq $(origin CC),...` rather than
+# `ifdef` since CC is one of the GNU make implicit variables. series
+#
+# See https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html
+ifeq ($(origin CC),default)
   ifneq ($(shell which gcc-6),)
     CC = gcc-6
   else ifneq ($(shell which gcc-5),)