diff --git a/master.cfg b/master.cfg
index 8c57e2b..163fbff 100644
--- a/master.cfg
+++ b/master.cfg
@@ -1291,8 +1291,8 @@ class RunTestGDBPlainAIX (RunTestGDBAIX_Common, RunTestGDBPlain_c64t64):
 class RunTestGDBPlainSolaris_c64 (BuildAndTestGDBFactory):
     """Compiling for Solaris"""
     def __init__ (self, **kwargs):
-        self.extra_CFLAGS += [ '-m64', '-O' ]
-        self.extra_CXXFLAGS += [ '-m64', '-O' ]
+        self.extra_CFLAGS = [ '-m64', '-O' ]
+        self.extra_CXXFLAGS = [ '-m64', '-O' ]
         self.enable_targets_all = False
         self.make_command = 'gmake'
         self.run_testsuite = False