Index: scripts/mk_util.py
--- scripts/mk_util.py.orig	2017-12-10 15:16:18.939458000 +0100
+++ scripts/mk_util.py	2017-12-10 15:16:55.913509000 +0100
@@ -2475,7 +2475,7 @@
             EXAMP_DEBUG_FLAG = '-g'
             CPPFLAGS     = '%s -DZ3DEBUG -D_DEBUG' % CPPFLAGS
         else:
-            CXXFLAGS     = '%s -O3' % CXXFLAGS
+            CXXFLAGS     = '%s -O2' % CXXFLAGS
             if GPROF:
                 CXXFLAGS     += '-fomit-frame-pointer'
             CPPFLAGS     = '%s -DNDEBUG -D_EXTERNAL_RELEASE' % CPPFLAGS
