diff --git a/App/tools/driver.makefile b/App/tools/driver.makefile
index dfcada4..513d111 100644
--- a/App/tools/driver.makefile
+++ b/App/tools/driver.makefile
@@ -531,6 +531,8 @@ endif
 
 # Add sources for specific epics types (3.13 or 3.14) or architectures.
 ARCH_PARTS = ${T_A} $(subst -, ,${T_A}) ${OS_CLASS}
+export ARCH_PARTS
+
 VAR_EXTENSIONS = $(firstword $(subst ., ,${EPICSVERSION})) ${EPICS_BASETYPE} ${EPICSVERSION} ${ARCH_PARTS} ${ARCH_PARTS:%=${EPICS_BASETYPE}_%} ${ARCH_PARTS:%=${EPICSVERSION}_%}
 export VAR_EXTENSIONS