--- a/GKlib/GKlibSystem.cmake
+++ b/GKlib/GKlibSystem.cmake
@@ -20,7 +20,7 @@
 elseif(MINGW)
   set(GKlib_COPTS "-DUSE_GKREGEX")
 else()
-  set(GKlib_COPTS "-O3")
+  set(GKlib_COPTS "")
   set(GKlib_COPTIONS "-DLINUX -D_FILE_OFFSET_BITS=64")
 endif(MSVC)
 if(CYGWIN)