diff --git a/master.cfg b/master.cfg
index 7df30ca..0d4b4a4 100644
--- a/master.cfg
+++ b/master.cfg
@@ -1049,8 +1049,8 @@ The parameters of the class are:
         if self.use_system_debuginfo:
             self.extra_conf_flags.append ('--with-separate-debug-dir=%s' % self.system_debuginfo_location)
 
-        self.extra_conf_flags.append ("CFLAGS=%s" % default_CFLAGS + ' '.join (self.extra_CFLAGS))
-        self.extra_conf_flags.append ("CXXFLAGS=%s" % default_CXXFLAGS + ' '.join (self.extra_CXXFLAGS))
+        self.extra_conf_flags.append ("CFLAGS=%s" % default_CFLAGS + " " + ' '.join (self.extra_CFLAGS))
+        self.extra_conf_flags.append ("CXXFLAGS=%s" % default_CXXFLAGS + " " + ' '.join (self.extra_CXXFLAGS))
         self.extra_conf_flags.append (architecture_triplet)
 
         self.addStep (self.ConfigureClass (self.extra_conf_flags, haltOnFailure = True))