diff --git a/configure/CONFIG b/configure/CONFIG
index 9f56fbbfb..1b3664bfd 100644
--- a/configure/CONFIG
+++ b/configure/CONFIG
@@ -25,8 +25,11 @@ else
 CONFIG ?= $(EPICS_BASE)/configure
 endif
 
-#
-EPICS_HOST_ARCH ?= $(shell $(CONFIG)/../startup/EpicsHostArch.pl)
+# Provide a default if the user hasn't set EPICS_HOST_ARCH
+ifeq ($(origin EPICS_HOST_ARCH), undefined)
+# NB: Must use a simply expanded variable here for performance:
+EPICS_HOST_ARCH := $(shell $(CONFIG)/../startup/EpicsHostArch.pl)
+endif
 #
 
 -include $(CONFIG)/os/CONFIG_COMPAT