diff --git a/deploy.sh b/deploy.sh
index 296902d..8529a85 100755
--- a/deploy.sh
+++ b/deploy.sh
@@ -1,10 +1,33 @@
 #!/usr/bin/env bash
+# The script creates a separate folder in build/ and creates tags there, pushes
+# them and then uploads the package to PyPI.
 
 set -eu -o pipefail
 
+cd CORRECT_FOLDER
+
+PROJECT_NAME=parso
+PROJECT=git-clone
+BRANCH=master
+FOLDER=build/$PROJECT
+
+cd $FOLDER
+git checkout $BRANCH
+
 # Create tag
-git tag v$(python -c 'import parso; print(parso.__version__)')
-git push --tags
+tag=v$(python -c "import $PROJECT_NAME; print($PROJECT_NAME.__version__)")
+
+master_ref=$(git show-ref -s $BRANCH)
+tag_ref=$(git show-ref -s $tag | true)
+if [ $tag_ref ]; then
+    if [ $tag_ref != $master_ref ]; then
+        echo 'Cannot tag something that has already been tagged with another commit.'
+        exit 1
+    fi
+else
+    git tag $BRANCH
+    git push --tags
+fi
 
 # Package and upload to PyPI
 rm -rf dist/