diff --git a/configure.ac b/configure.ac
index 0af46b16..38965fbb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -27,7 +27,7 @@ case $host_os in
 esac
 
 # Checks the flags.
-CFLAGS="-DIDEVICERESTORE_NOMAIN=1 -DTSSCHECKER_NOMAIN=1"
+CFLAGS+=" -DIDEVICERESTORE_NOMAIN=1 -DTSSCHECKER_NOMAIN=1"
 CXXFLAGS+=" -std=c++11"
 CFLAGS+=" -std=c11"