diff --git a/bin/fmt.sh b/bin/fmt.sh
index 2524175..593a279 100755
--- a/bin/fmt.sh
+++ b/bin/fmt.sh
@@ -48,6 +48,13 @@ trailing_whitespace() {
   sh_c find . -name "'*.sedbak'" -delete
 }
 
+d2fmt() {
+  if ! command -v d2 /dev/null && [ -n "${CI-}" ]; then
+    curl -fsSL https://d2lang.com/install.sh | sh -s --
+  fi
+  sh_c hide XARGS_N=1 xargsd "'\.\(d2\)$'" d2 fmt
+}
+
 main() {
   job_parseflags "$@"
   ensure_changed_files
@@ -69,6 +76,9 @@ main() {
   if <"$CHANGED_FILES" grep -q '\.\(js\|jsx\|ts\|tsx\|scss\|css\|html\)$'; then
     runjob prettier &
   fi
+  if <"$CHANGED_FILES" grep -qm1 '\.\(d2\)$'; then
+    runjob d2fmt &
+  fi
   waitjobs
 }