--- a/SConstruct
+++ b/SConstruct
@@ -972,7 +972,6 @@ if meta.compiler in ['gcc', 'clang']:
         for var in ['CXXFLAGS', 'CFLAGS']:
             env.Append(**{var: [
                 '-fvisibility=hidden',
-                '-O3',
             ]})
 
     if meta.compiler == 'gcc' and meta.compiler_ver[:2] < (4, 6):
@@ -990,10 +989,7 @@ if meta.compiler in ['cc']:
                 '-g',
             ]})
     else:
-        for var in ['CXXFLAGS', 'CFLAGS']:
-            env.Append(**{var: [
-                '-O3',
-            ]})
+        pass
 
     for var in ['CXXFLAGS', 'CFLAGS']:
         conf.env.Append(**{var: [