diff --git a/themes/agnoster.zsh-theme b/themes/agnoster.zsh-theme
index 8c700d06a..b0a3b7b3f 100644
--- a/themes/agnoster.zsh-theme
+++ b/themes/agnoster.zsh-theme
@@ -106,7 +106,7 @@ prompt_git() {
   }
   local ref dirty mode repo_path
 
-  if $(git rev-parse --is-inside-work-tree >/dev/null 2>&1); then
+   if [[ "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ]]; then
     repo_path=$(git rev-parse --git-dir 2>/dev/null)
     dirty=$(parse_git_dirty)
     ref=$(git symbolic-ref HEAD 2> /dev/null) || ref="➦ $(git rev-parse --short HEAD 2> /dev/null)"