diff --git a/release/Makefile.inc1 b/release/Makefile.inc1
index 64f7c6e049a4..a97dee9994b6 100644
--- a/release/Makefile.inc1
+++ b/release/Makefile.inc1
@@ -40,3 +40,6 @@ BUILDDATE!=		date +%Y%m%d
 .export BUILDDATE
 .endif
 
+# Override UNAME_r to allow building ports for a different branch.
+UNAME_r=	${REVISION}-${BRANCH}
+.export UNAME_r
diff --git a/release/Makefile.vm b/release/Makefile.vm
index b0bd47521dc5..cad1974e3a6f 100644
--- a/release/Makefile.vm
+++ b/release/Makefile.vm
@@ -54,7 +54,7 @@ emulator-portinstall:
 .if ( ${TARGET_ARCH} != "i386" ) || ( ${MACHINE_ARCH} != "amd64" )
 .if !exists(/usr/local/bin/qemu-${TARGET_ARCH}-static)
 .if exists(${PORTSDIR}/emulators/qemu-user-static/Makefile)
-	env - UNAME_r="${REVISION}-${BRANCH}" PATH=$$PATH make -C ${PORTSDIR}/emulators/qemu-user-static BATCH=1 all install clean
+	env - UNAME_r=${UNAME_r} PATH=$$PATH make -C ${PORTSDIR}/emulators/qemu-user-static BATCH=1 all install clean
 .else
 .if !exists(/usr/local/sbin/pkg-static)
 	env ASSUME_ALWAYS_YES=yes pkg bootstrap -y