diff --git a/README.md b/README.md
index 2782ade..f132efb 100644
--- a/README.md
+++ b/README.md
@@ -64,7 +64,7 @@ It will tell you what it's done, so it should look something like this:
 + echo '*.jpeg diff=image' >>'/Users/yourname/.gitattributes'
 + echo '*.jpg diff=image' >>'/Users/yourname/.gitattributes'
 + echo '*.png diff=image' >>'/Users/yourname/.gitattributes'
-+ git config --global alias.diff-image '!f() { GIT_DIFF_IMAGE_ENABLED=1 git diff "$@"; }; f'
++ git config --global alias.diff-image '!f() { cd -- "${GIT_PREFIX:-.}"; GIT_DIFF_IMAGE_ENABLED=1 git diff "$@"; }; f'
 + git config --global diff.image.command '~/git-diff-image/git_diff_image'
 ```
 
diff --git a/install.sh b/install.sh
index a9bd69d..3fb7f03 100755
--- a/install.sh
+++ b/install.sh
@@ -69,8 +69,8 @@ addattr jpeg
 addattr jpg
 addattr png
 
-echo '+ git config --global alias.diff-image '"'"'!f() { GIT_DIFF_IMAGE_ENABLED=1 git diff "$@"; }; f'"'"
-git config --global alias.diff-image '!f() { GIT_DIFF_IMAGE_ENABLED=1 git diff "$@"; }; f'
+echo '+ git config --global alias.diff-image '"'"'!f() { cd -- "${GIT_PREFIX:-.}"; GIT_DIFF_IMAGE_ENABLED=1 git diff "$@"; }; f'"'"
+git config --global alias.diff-image '!f() { cd -- "${GIT_PREFIX:-.}"; GIT_DIFF_IMAGE_ENABLED=1 git diff "$@"; }; f'
 
 echo "+ git config --global diff.image.command '$thisdir_tilde/git_diff_image'"
 git config --global diff.image.command "$thisdir_tilde/git_diff_image"