diff --git a/configure/CONFIG b/configure/CONFIG
index 9d8d7e04b..f5ba0b780 100644
--- a/configure/CONFIG
+++ b/configure/CONFIG
@@ -20,14 +20,15 @@ else
 endif
 
 # Provide a default if the user hasn't set EPICS_HOST_ARCH
+#
 ifeq ($(origin EPICS_HOST_ARCH), undefined)
   # Bootstrapping ...
-  EHA = $(firstword $(wildcard $(EPICS_BASE)/lib/perl/EpicsHostArch.pl \
+  EHA := $(firstword $(wildcard $(EPICS_BASE)/lib/perl/EpicsHostArch.pl \
         $(TOP)/src/tools/EpicsHostArch.pl))
   # NB: We use a simply expanded variable here for performance:
   export EPICS_HOST_ARCH := $(shell perl $(EHA))
+  undefine EHA
 endif
-#
 
 -include $(CONFIG)/os/CONFIG_COMPAT