--- eclass/multilib.eclass
+++ eclass/multilib.eclass
@@ -397,7 +397,12 @@
 	if [[ ${__DEFAULT_ABI_SAVED} == "true" ]] ; then
 		for v in CHOST CBUILD AS CC CXX LD PKG_CONFIG_{LIBDIR,PATH} ; do
 			vv="__abi_saved_${v}"
-			export ${v}="${!vv}"
+			# preserve unset variables
+			if [[ ${!vv} == "__unset__" ]] ; then
+				unset ${v}
+			else
+				export ${v}="${!vv}"
+			fi
 			unset ${vv}
 		done
 		unset __DEFAULT_ABI_SAVED
@@ -408,7 +413,12 @@
 	if [[ ${ABI} != ${DEFAULT_ABI} ]] ; then
 		# Back that multilib-ass up so we can restore it later
 		for v in CHOST CBUILD AS CC CXX LD PKG_CONFIG_{LIBDIR,PATH} ; do
-			export __abi_saved_${v}="${!v}"
+			# preserve unset variables
+			if [[ -z ${!v+x} ]] ; then
+				export __abi_saved_${v}="__unset__"
+			else
+				export __abi_saved_${v}="${!v}"
+			fi
 		done
 		export __DEFAULT_ABI_SAVED="true"