diff --git a/tools/install_gcc_539 b/tools/install_gcc_539
index ab14191..bcc222d 100755
--- a/tools/install_gcc_539
+++ b/tools/install_gcc_539
@@ -16,6 +16,8 @@ if [ "`which gmake`" != "" ]; then
         MAKE=gmake
 fi
 
+export CFLAGS="-O2 -pipe -std=gnu89"
+
 while read a
 do
   echo "$a"
diff --git a/tools/install_gcc_539_thumb b/tools/install_gcc_539_thumb
index 37ae9b9..2110e8e 100755
--- a/tools/install_gcc_539_thumb
+++ b/tools/install_gcc_539_thumb
@@ -16,6 +16,8 @@ if [ "`which gmake`" != "" ]; then
         MAKE=gmake
 fi
 
+export CFLAGS="-O2 -pipe -std=gnu89"
+
 while read a
 do
   echo "$a"