diff --git a/gcc/configure b/gcc/configure
index e7f85b78ad992ed457370accfe92ff4ca244b71f..2754293d661ce0846d5bcb89381993ca691815b4 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -5473,12 +5473,28 @@ ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ex
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
 
-# Remove the -O2: for historical reasons, unless bootstrapping we prefer
+# Remove all -O flags: for historical reasons, unless bootstrapping we prefer
 # optimizations to be activated explicitly by the toplevel.
 case "$CC" in
   */prev-gcc/xgcc*) ;;
-  *) CFLAGS=`echo "$CFLAGS " | sed -e "s/-Ofast[ 	]//" -e "s/-O[gs][ 	]//" -e "s/[^,]-O[0-9]*[ 	]//" `
-     CXXFLAGS=`echo "$CXXFLAGS " | sed -e "s/-Ofast[ 	]//" -e "s/-O[gs][ 	]//" -e "s/[^,]-O[0-9]*[ 	]//" ` ;;
+  *)
+    new_CFLAGS=
+    for flag in $CFLAGS; do
+      case $flag in
+	-O*) ;;
+	*) new_CFLAGS="$new_CFLAGS $flag" ;;
+      esac
+    done
+    CFLAGS=$new_CFLAGS
+    new_CXXFLAGS=
+    for flag in $CXXFLAGS; do
+      case $flag in
+	-O*) ;;
+	*) new_CXXFLAGS="$new_CXXFLAGS $flag" ;;
+      esac
+    done
+    CXXFLAGS=$new_CXXFLAGS
+    ;;
 esac
 
 
@@ -21461,7 +21477,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 21464 "configure"
+#line 21480 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -21567,7 +21583,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 21570 "configure"
+#line 21586 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
diff --git a/gcc/configure.ac b/gcc/configure.ac
index e9bddc6db21f2db52c457bed74de2253b99c614a..ed8d9596668bb6ef711b50eaf1176a003294ca79 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -463,12 +463,28 @@ ACX_PROG_GDC([-I"$srcdir"/d])
 # Do configure tests with the C++ compiler, since that's what we build with.
 AC_LANG(C++)
 
-# Remove the -O2: for historical reasons, unless bootstrapping we prefer
+# Remove all -O flags: for historical reasons, unless bootstrapping we prefer
 # optimizations to be activated explicitly by the toplevel.
 case "$CC" in
   */prev-gcc/xgcc*) ;;
-  *) CFLAGS=`echo "$CFLAGS " | sed -e "s/-Ofast[[ 	]]//" -e "s/-O[[gs]][[ 	]]//" -e "s/[[^,]]-O[[0-9]]*[[ 	]]//" `
-     CXXFLAGS=`echo "$CXXFLAGS " | sed -e "s/-Ofast[[ 	]]//" -e "s/-O[[gs]][[ 	]]//" -e "s/[[^,]]-O[[0-9]]*[[ 	]]//" ` ;;
+  *)
+    new_CFLAGS=
+    for flag in $CFLAGS; do
+      case $flag in
+	-O*) ;;
+	*) new_CFLAGS="$new_CFLAGS $flag" ;;
+      esac
+    done
+    CFLAGS=$new_CFLAGS
+    new_CXXFLAGS=
+    for flag in $CXXFLAGS; do
+      case $flag in
+	-O*) ;;
+	*) new_CXXFLAGS="$new_CXXFLAGS $flag" ;;
+      esac
+    done
+    CXXFLAGS=$new_CXXFLAGS
+    ;;
 esac
 AC_SUBST(CFLAGS)
 AC_SUBST(CXXFLAGS)