diff --git a/bootstrap b/bootstrap
index 92d458f..3352589 100755
--- a/bootstrap
+++ b/bootstrap
@@ -1,4 +1,4 @@
-# !/bin/sh -e
+#!/bin/sh -e
 
 if [ `uname -s` = "Darwin" ]; then
 echo "WARNING: OSX autogen build is not supported"
@@ -13,20 +13,22 @@
 
 # If libtool is not installed -> "error: Libtool library used but 'LIBTOOL' is undefined"
 
+if [ ! -e "./m4" ]; then
 mkdir m4 2>/dev/null
+fi
 
 BROTLI_ABI_HEX=`sed -n 's/#define BROTLI_ABI_VERSION 0x//p' c/common/version.h`
 BROTLI_ABI_INT=`echo "ibase=16;$BROTLI_ABI_HEX" | bc`
-BROTLI_ABI_CURRENT=`expr $BROTLI_ABI_INT / 16777216`
-BROTLI_ABI_REVISION=`expr $BROTLI_ABI_INT / 4096 % 4096`
-BROTLI_ABI_AGE=`expr $BROTLI_ABI_INT % 4096`
+BROTLI_ABI_CURRENT=`echo "$BROTLI_ABI_INT / 16777216" | bc`
+BROTLI_ABI_REVISION=`echo "$BROTLI_ABI_INT / 4096 % 4096" | bc`
+BROTLI_ABI_AGE=`echo "$BROTLI_ABI_INT % 4096" | bc`
 BROTLI_ABI_INFO="$BROTLI_ABI_CURRENT:$BROTLI_ABI_REVISION:$BROTLI_ABI_AGE"
 
 BROTLI_VERSION_HEX=`sed -n 's/#define BROTLI_VERSION 0x//p' c/common/version.h`
 BROTLI_VERSION_INT=`echo "ibase=16;$BROTLI_VERSION_HEX" | bc`
-BROTLI_VERSION_MAJOR=`expr $BROTLI_VERSION_INT / 16777216`
-BROTLI_VERSION_MINOR=`expr $BROTLI_VERSION_INT / 4096 % 4096`
-BROTLI_VERSION_PATCH=`expr $BROTLI_VERSION_INT % 4096`
+BROTLI_VERSION_MAJOR=`echo "$BROTLI_VERSION_INT / 16777216" | bc`
+BROTLI_VERSION_MINOR=`echo "$BROTLI_VERSION_INT / 4096 % 4096" | bc`
+BROTLI_VERSION_PATCH=`echo "$BROTLI_VERSION_INT % 4096" | bc`
 BROTLI_VERSION="$BROTLI_VERSION_MAJOR.$BROTLI_VERSION_MINOR.$BROTLI_VERSION_PATCH"
 
 sed -i.bak -r "s/[0-9]+:[0-9]+:[0-9]+/$BROTLI_ABI_INFO/" Makefile.am