diff --git a/README.md b/README.md
index c8a374e..e2731dd 100755
--- a/README.md
+++ b/README.md
@@ -242,7 +242,7 @@ follows:
  * Run build.sh to build all stages
  * Add SKIP files to the earlier successfully built stages
  * Modify the last stage
- * Rebuild just the last stage using ```sudo CLEAN=1 ./build.sh```
+ * Rebuild just the last stage using ```sudo ./build.sh```
  * Once you're happy with the image you can remove the SKIP_IMAGES files and
    export your image to test
 
diff --git a/build.sh b/build.sh
index f0597b7..32d203b 100755
--- a/build.sh
+++ b/build.sh
@@ -143,7 +143,7 @@ export LOG_FILE="${WORK_DIR}/build.log"
 
 export BASE_DIR
 
-export CLEAN
+export CLEAN=${CLEAN:-"1"}
 export IMG_NAME
 export APT_PROXY