diff --git a/scripts/devshell/prettify b/scripts/devshell/prettify
index e18b0d8eee..60db957899 100755
--- a/scripts/devshell/prettify
+++ b/scripts/devshell/prettify
@@ -6,24 +6,26 @@ show_help() {
     echo "Format Haskell source files using fourmolu and stylish-haskell."
     echo ""
     echo "Options:"
-    echo "  -t, --tracked     Format all tracked Haskell (*.hs) files in the repository"
-    echo "  -s, --staged      Format all staged Haskell (*.hs) files"
-    echo "  -m, --modified    Format all modified Haskell (*.hs) files, including staged and unstaged"
-    echo "  -n, --not-staged  Format all non-staged modified Haskell (*.hs) files"
-    echo "  -h, --help        Show this help message"
+    echo "  -t, --tracked           Format all tracked Haskell (*.hs) files in the repository"
+    echo "  -s, --staged            Format all staged Haskell (*.hs) files"
+    echo "  -m, --modified          Format all modified Haskell (*.hs) files, including staged and unstaged"
+    echo "  -n, --not-staged        Format all non-staged modified Haskell (*.hs) files"
+    echo "  -p, --previous-commit   Format all Haskell (*.hs) files modified before the last commit (HEAD~1)"
+    echo "  -h, --help              Show this help message"
 }
 
 # Function to run the formatting commands
 run_format() {
+    top_level=$(git rev-parse --show-toplevel) 
     for file in "$@"; do
         if [[ $file == *.hs ]]; then
-            if grep -qE '^#' "$file"; then
+            if grep -qE '^#' "$top_level/$file"; then
               echo "$file contains CPP.  Skipping."
             else
               echo "Formatting: $file"
-              fourmolu -q -i "$file"
-              fourmolu -q -i "$file"
-              stylish-haskell -i "$file"
+              fourmolu -q -i "$top_level/$file"
+              fourmolu -q -i "$top_level/$file"
+              stylish-haskell -i "$top_level/$file"
             fi
         fi
     done
@@ -45,6 +47,9 @@ case $1 in
     -n|--not-staged)
         files=$(git diff --name-only --diff-filter=ACM '*.hs')
         ;;
+    -p|--previous-commit)
+        files=$(git diff --name-only --diff-filter=ACM HEAD~1 '*.hs')
+        ;;
     -h|--help)
         show_help
         exit 0