diff --git a/commands/host/_lib/upsun-disk-helper.sh b/commands/host/_lib/upsun-disk-helper.sh
index d388f4a..5fdf0b7 100644
--- a/commands/host/_lib/upsun-disk-helper.sh
+++ b/commands/host/_lib/upsun-disk-helper.sh
@@ -1,5 +1,26 @@
 #ddev-generated
 #annertech-ddev
+
+# GNU numfmt is not on macOS. Print an IEC size (1024) with two decimals.
+format_iec() {
+    local value="$1"
+    local from_unit="${2:-1}"
+    python3 - "$value" "$from_unit" << 'PY'
+import sys
+n = int(sys.argv[1]) * int(sys.argv[2])
+units = ["", "K", "M", "G", "T", "P"]
+i = 0
+v = float(n)
+while abs(v) >= 1024 and i < len(units) - 1:
+    v /= 1024.0
+    i += 1
+if i == 0:
+    print(str(int(v)))
+else:
+    print(f"{v:.2f}{units[i]}")
+PY
+}
+
 upsun_disk_helper() {
     local project_id="$1"
     local project_name="$2"
@@ -24,11 +45,11 @@ upsun_disk_helper() {
 
     echo ""
     echo "Total assigned (app+mysqldb+solrsearch):"
-    numfmt --to iec --format "%3.2f" "$total_assigned"
+    format_iec "$total_assigned"
 
     echo ""
     echo "Total storage available in project:"
-    numfmt --from-unit=1048576 --to iec --format="%3.2f" "$total_available"
+    format_iec "$total_available" 1048576
 
     echo_yellow ""
     echo_yellow "WARNING: command uses hardcoded values for service totals. Verify numbers with table above!"
diff --git a/tests/upsun-disk-darwin.test.sh b/tests/upsun-disk-darwin.test.sh
new file mode 100644
index 0000000..86b9939
--- /dev/null
+++ b/tests/upsun-disk-darwin.test.sh
@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -euo pipefail
+root=$(cd "$(dirname "$0")/.." && pwd)
+helper="$root/commands/host/_lib/upsun-disk-helper.sh"
+
+set +e
+numfmt --to iec --format "%3.2f" 1048576 >/tmp/numfmt.out 2>/tmp/numfmt.err
+red=$?
+set -e
+if [ "$red" -eq 0 ]; then
+  echo "numfmt unexpectedly succeeded" >&2
+  exit 1
+fi
+grep -q "command not found" /tmp/numfmt.err
+
+funcs=$(awk '
+  /^format_iec\(\) \{/ {p=1}
+  p {print}
+  /^}$/ && p {exit}
+' "$helper")
+eval "$funcs"
+one=$(format_iec 1048576)
+five=$(format_iec 5 1048576)
+small=$(format_iec 1536)
+[ "$one" = "1.00M" ]
+[ "$five" = "5.00M" ]
+[ "$small" = "1.50K" ]
+if grep -Eq '^[^#]*numfmt ' "$helper"; then
+  echo "helper still calls numfmt" >&2
+  exit 1
+fi
+echo "upsun disk darwin ok (numfmt exit $red, 1MiB $one, 5 units $five)"