diff --git a/plug.vim b/plug.vim
index 866db9c..ff1827b 100644
--- a/plug.vim
+++ b/plug.vim
@@ -705,6 +705,12 @@ function! s:prepare(...)
     throw 'Invalid current working directory. Cannot proceed.'
   endif
 
+  for evar in ['$GIT_DIR', '$GIT_WORK_TREE']
+    if exists(evar)
+      throw evar.' detected. Cannot proceed.'
+    endif
+  endfor
+
   call s:job_abort()
   if s:switch_in()
     normal q