diff --git a/configure.ac b/configure.ac
index 7066849c1eb75..ca81784a227db 100644
--- a/configure.ac
+++ b/configure.ac
@@ -794,8 +794,9 @@ if test "$PHP_GCOV" = "yes"; then
 
   dnl Remove all optimization flags from CFLAGS.
   changequote({,})
-  CFLAGS=`echo "$CFLAGS" | "${SED}" -e 's/-O[0-9s]*//g'`
-  CXXFLAGS=`echo "$CXXFLAGS" | "${SED}" -e 's/-O[0-9s]*//g'`
+  dnl Discard known '-O...' flags, including just '-O', but do not remove only '-O' in '-Ounknown'
+  CFLAGS=`echo "$CFLAGS" | $SED -e 's/-O\([0-9gsz]\|fast\|\)\([\t ]\|$\)//g'`
+  CXXFLAGS=`echo "$CXXFLAGS" | $SED -e 's/-O\([0-9gsz]\|fast\|\)\([\t ]\|$\)//g'`
   changequote([,])
 
   dnl Add the special gcc flags.
@@ -814,8 +815,9 @@ if test "$PHP_DEBUG" = "yes"; then
   PHP_DEBUG=1
   ZEND_DEBUG=yes
   changequote({,})
-  CFLAGS=`echo "$CFLAGS" | "${SED}" -e 's/-O[0-9s]*//g'`
-  CXXFLAGS=`echo "$CXXFLAGS" | "${SED}" -e 's/-O[0-9s]*//g'`
+  dnl Discard known '-O...' flags, including just '-O', but do not remove only '-O' in '-Ounknown'
+  CFLAGS=`echo "$CFLAGS" | $SED -e 's/-O\([0-9gsz]\|fast\|\)\([\t ]\|$\)//g'`
+  CXXFLAGS=`echo "$CXXFLAGS" | $SED -e 's/-O\([0-9gsz]\|fast\|\)\([\t ]\|$\)//g'`
   changequote([,])
   dnl Add -O0 only if GCC or ICC is used.
   if test "$GCC" = "yes" || test "$ICC" = "yes"; then
diff --git a/scripts/phpize.m4 b/scripts/phpize.m4
index 616d16420a5a1..14bcde45f03a3 100644
--- a/scripts/phpize.m4
+++ b/scripts/phpize.m4
@@ -116,8 +116,9 @@ if test "$PHP_DEBUG" = "yes"; then
   PHP_DEBUG=1
   ZEND_DEBUG=yes
   changequote({,})
-  CFLAGS=`echo "$CFLAGS" | $SED -e 's/-O[0-9s]*//g'`
-  CXXFLAGS=`echo "$CXXFLAGS" | $SED -e 's/-O[0-9s]*//g'`
+  dnl Discard known '-O...' flags, including just '-O', but do not remove only '-O' in '-Ounknown'
+  CFLAGS=`echo "$CFLAGS" | $SED -e 's/-O\([0-9gsz]\|fast\|\)\([\t ]\|$\)//g'`
+  CXXFLAGS=`echo "$CXXFLAGS" | $SED -e 's/-O\([0-9gsz]\|fast\|\)\([\t ]\|$\)//g'`
   changequote([,])
   dnl Add -O0 only if GCC or ICC is used.
   if test "$GCC" = "yes" || test "$ICC" = "yes"; then