diff --git a/cros_workon b/cros_workon
index 128933a84a..e9400da47d 100755
--- a/cros_workon
+++ b/cros_workon
@@ -148,6 +148,25 @@ regen_manifest_and_sync() {
   find_repo_dir
   local_manifest="${REPODIR}/local_manifest.xml"
 
+  # ensure we don't clobber existing manifest entries
+  if [ -f "${local_manifest}" ]; then
+      grep -q -i "<remote" "${local_manifest}"
+      if [ $? -ne 1 ]; then
+	  die "Your local manifest will be clobbered running cros_workon. You can not have any <remote> tags at all."
+      fi
+      sed -ne '/^[[:space:]]\+[^[:space:]]/q1' "${local_manifest}"
+      if [ $? -ne 0 ]; then
+	  die "Your local manifest will be clobbered running cros_workon. You can not have any tags that span multiple lines or are indented."
+      fi
+      egrep -q "^[^<]" "${local_manifest}" 
+      if [ $? -ne 1 ]; then
+	  die "Your local manifest will be clobbered running cros_workon. You can not have any tags that span multiple lines"
+      fi
+      grep -v "<project" "${local_manifest}" | grep -q -i "<project" 
+      if [ $? -eq 0 ]; then
+	  die "Your local manifest has mixed case tags for project.  You can not have mixed case tags"
+      fi
+  fi
   # preserve old manifest entries
   [ -f "${local_manifest}" ] && \
     MANIFEST_ENTRIES_OLD=$(cat "${local_manifest}" | grep "^<project")