diff --git a/qrexec/Makefile b/qrexec/Makefile
index 443ef0c..c72be00 100644
--- a/qrexec/Makefile
+++ b/qrexec/Makefile
@@ -1,7 +1,7 @@
-CC=gcc
-CFLAGS+=-I. -g -O2 -Wall -Wextra -Werror -pie -fPIC `pkg-config --cflags vchan-$(BACKEND_VMM)`
-LDFLAGS=-pie
-LDLIBS=`pkg-config --libs vchan-$(BACKEND_VMM)` -lqrexec-utils -lpam
+CC ?= gcc
+CFLAGS += -I. -g -O2 -Wall -Wextra -Werror -pie -fPIC `pkg-config --cflags vchan-$(BACKEND_VMM)`
+LDFLAGS += -pie
+LDLIBS = `pkg-config --libs vchan-$(BACKEND_VMM)` -lqrexec-utils -lpam
 
 all: qrexec-agent qrexec-client-vm qrexec-fork-server
 qrexec-agent: qrexec-agent.o qrexec-agent-data.o
diff --git a/rpm_spec/core-agent.spec.in b/rpm_spec/core-agent.spec.in
index a3578e3..1778046 100644
--- a/rpm_spec/core-agent.spec.in
+++ b/rpm_spec/core-agent.spec.in
@@ -269,6 +269,7 @@ Thunar support for Qubes VM tools
 %setup -q
 
 %build
+%{?set_build_flags}
 for dir in qubes-rpc qrexec misc; do
   make -C $dir BACKEND_VMM=@BACKEND_VMM@
 done