--- a/configure.ac
+++ b/configure.ac
@@ -137,8 +137,7 @@
 AC_SUBST(HOST_OS)
 # ====================================================================
 
-CFLAGS="${CFLAGS} -O3"
-CXXFLAGS="${CXXFLAGS} -O3 -Wall"
+CXXFLAGS="${CXXFLAGS} -Wall"
 
 # The std=c11 flag provides the proper float-pt math decls working,
 # e.g. fmax  However, it also undefined _BSD_SOURCE, etc. which is
@@ -908,10 +907,6 @@
 
 AC_FUNC_STRERROR_R
 
-AC_SUBST(CFLAGS)
-AC_SUBST(CPPFLAGS)
-AC_SUBST(CXXFLAGS)
-
 dnl Save the compilation definitions for an extended version printout
 AC_OUTPUT_MAKE_DEFS()
 LG_DEFS=`$ECHO "$DEFS" | $SED 's/\\\\//g'`
