diff --git a/libga68/configure b/libga68/configure
index 731476fc9095..1208c3fa616d 100755
--- a/libga68/configure
+++ b/libga68/configure
@@ -5906,7 +5906,9 @@ $as_echo "$ac_try_echo"; } >&5
   rm -f conftest.er1 conftest.err
   $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
   test $ac_status = 0; }
-A68FLAGS="-g -O2"
+if test -z "$A68FLAGS"; then
+  A68FLAGS="-g -O2"
+fi
 ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
diff --git a/libga68/m4/autoconf.m4 b/libga68/m4/autoconf.m4
index 7b85996265c0..daf67322f35e 100644
--- a/libga68/m4/autoconf.m4
+++ b/libga68/m4/autoconf.m4
@@ -126,6 +126,8 @@ ac_compiler=$[2]
 _AC_DO_LIMIT([$ac_compiler --version >&AS_MESSAGE_LOG_FD])
 m4_expand_once([_AC_COMPILER_EXEEXT])[]dnl
 m4_expand_once([_AC_COMPILER_OBJEXT])[]dnl
-A68FLAGS="-g -O2"
+if test -z "$A68FLAGS"; then
+  A68FLAGS="-g -O2"
+fi
 AC_LANG_POP(Algol 68)dnl
 ])# AC_PROG_A68