diff --git a/themes/agnoster.zsh-theme b/themes/agnoster.zsh-theme
index 103041eef..da1f9b6e6 100644
--- a/themes/agnoster.zsh-theme
+++ b/themes/agnoster.zsh-theme
@@ -128,6 +128,7 @@ prompt_git() {
 }
 
 prompt_hg() {
+  (( $+commands[hg] )) || return
   local rev status
   if $(hg id >/dev/null 2>&1); then
     if $(hg prompt >/dev/null 2>&1); then