diff --git a/waflib/Tools/c_config.py b/waflib/Tools/c_config.py
index 80eaad66..8a6e2c28 100644
--- a/waflib/Tools/c_config.py
+++ b/waflib/Tools/c_config.py
@@ -195,7 +195,7 @@ def parse_flags(self, line, uselib_store, env=None, force_static=False, posix=No
 			static = False
 		elif x.startswith('-Wl'):
 			app('LINKFLAGS', x)
-		elif x.startswith(('-m', '-f', '-dynamic')):
+		elif x.startswith(('-m', '-f', '-dynamic', '-O')):
 			app('CFLAGS', x)
 			app('CXXFLAGS', x)
 		elif x.startswith('-bundle'):
@@ -210,9 +210,6 @@ def parse_flags(self, line, uselib_store, env=None, force_static=False, posix=No
 			app('LINKFLAGS', tmp)
 		elif x.endswith(('.a', '.so', '.dylib', '.lib')):
 			appu('LINKFLAGS', x) # not cool, #762
-		elif x.startswith('-O'):
-			app('CFLAGS', x)
-			app('CXXFLAGS', x)
 
 @conf
 def validate_cfg(self, kw):