diff --git a/antigen.zsh b/antigen.zsh
index 63d3a3b..2ffb667 100644
--- a/antigen.zsh
+++ b/antigen.zsh
@@ -316,11 +316,16 @@ antigen-revert () {
 # "what's new" message.
 antigen-selfupdate () {
     ( cd $_ANTIGEN_INSTALL_DIR
-        if [[ ! -d .git ]]; then
+        if [[ ! ( -d .git || -f .git ) ]]; then
             echo "Your copy of antigen doesn't appear to be a git clone. " \
                 "The 'selfupdate' command cannot work in this case."
             return 1
         fi
+        local head="$(git rev-parse --abbrev-ref HEAD)"
+        if [[ $head == "HEAD" ]]; then
+            # If current head is detached HEAD, checkout to master branch.
+            git checkout master
+        fi
         git pull
     )
 }