diff --git a/src/hudLocalityFormat.js b/src/hudLocalityFormat.js
index 697075a82..b9b8c3ea0 100644
--- a/src/hudLocalityFormat.js
+++ b/src/hudLocalityFormat.js
@@ -8,7 +8,10 @@ import { formatNumber, getLocale, t } from './i18n/index.js';
 import { unitLabel } from './ui/unitLabels.js';
 import { localizePlaceName } from './ui/placeNames.js';
 
-/** An upper-case HUD quantity such as `13KM` / `13КМ`, in the active language. */
+/**
+ * An upper-case HUD quantity such as `13KM` / `13КМ`, in the active language.
+ * Chinese and Japanese have no case and keep the catalog's `13 km`.
+ */
 export function hudQuantity(value, unit, digits = 0) {
   const number = formatNumber(value, {
     useGrouping: false,
@@ -16,7 +19,7 @@ export function hudQuantity(value, unit, digits = 0) {
     maximumFractionDigits: digits,
   });
   const label = unitLabel(unit);
-  if (getLocale().startsWith('zh-'))
+  if (/^(zh|ja)(-|$)/.test(getLocale()))
     return label ? `${number} ${label}` : number;
   return `${number}${label.toUpperCase()}`;
 }
diff --git a/src/i18n/ja-hud-units.test.mjs b/src/i18n/ja-hud-units.test.mjs
new file mode 100644
index 000000000..73568d0ce
--- /dev/null
+++ b/src/i18n/ja-hud-units.test.mjs
@@ -0,0 +1,22 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { setLocale } from './index.js';
+import { hudQuantity, LOCALIZED_LOCALITY } from '../hudLocalityFormat.js';
+import { formatCockpitDistance } from '../ui/cockpitPresentation.js';
+
+// revmain-opus-ja-i1-1: ja has no case, so HUD units keep the catalog case
+// (km), as the cockpit already does and docs/translations/ja.md requires.
+test('Japanese HUD units keep their case, like the cockpit', () => {
+  try {
+    setLocale('ja');
+    assert.equal(formatCockpitDistance(14000), '14 km');
+    assert.equal(hudQuantity(13, 'km'), '13 km');
+    assert.equal(hudQuantity(1.5, 'km', 1), '1.5 km');
+    assert.equal(
+      LOCALIZED_LOCALITY.near({ poi: 'Shibuya', city: 'Tokyo', distKm: 13 }),
+      'SHIBUYA（東京）付近 13 km',
+    );
+  } finally {
+    setLocale('en');
+  }
+});
diff --git a/src/i18n/locales/ja.json b/src/i18n/locales/ja.json
index 02e49d22a..b7c045555 100644
--- a/src/i18n/locales/ja.json
+++ b/src/i18n/locales/ja.json
@@ -803,8 +803,8 @@
   "DATE UNAVAILABLE": "日付不明",
   "UNSPECIFIED OPERATOR": "運用者未指定",
   "Select {mission}": "{mission}を選択",
-  "{value} KM": "{value} KM",
-  "{value} KM/S": "{value} KM/S",
+  "{value} KM": "{value} km",
+  "{value} KM/S": "{value} km/s",
   "Selected Space Mission": "選択中の宇宙ミッション",
   "SELECTED SPACE MISSION": "選択中の宇宙ミッション",
   "Show all missions": "すべてのミッションを表示",
@@ -1607,7 +1607,7 @@
   "REGION UNAVAILABLE": "地域を取得できません",
   "NO RECENT LOCATION MATCHES": "この地域の最近のニュースなし",
   "{domain} · {age}": "{domain} · {age}",
-  "{value} KM/H": "{value} KM/H",
+  "{value} KM/H": "{value} km/h",
   "CLOUD {pct}%": "雲量 {pct}%",
   "CLOUD UNKNOWN": "雲量不明",
   "{source} · LOCATION QUERY": "{source} · 位置クエリ",
diff --git a/src/i18n/same-as-english.json b/src/i18n/same-as-english.json
index 9ee97a600..73443c29e 100644
--- a/src/i18n/same-as-english.json
+++ b/src/i18n/same-as-english.json
@@ -169,9 +169,6 @@
     "{source} HTTP {status}",
     "{speed} kn",
     "{type}  SPD: {speed}  HDG: {heading}",
-    "{value} KM",
-    "{value} KM/H",
-    "{value} KM/S",
     "ΔE",
     "ΔN",
     "▲ {frp} MW"
diff --git a/src/i18n/zh-CN-display.test.mjs b/src/i18n/zh-CN-display.test.mjs
index b9e55058d..db85662c4 100644
--- a/src/i18n/zh-CN-display.test.mjs
+++ b/src/i18n/zh-CN-display.test.mjs
@@ -17,6 +17,9 @@ test('Chinese HUD and cockpit units keep their case without spacing coordinates'
     assert.equal(formatCockpitDistance(14000), '14\u00a0km');
     assert.equal(LOCALIZED_LOCALITY.sector({ latDeg: 21.33, lonDeg: -77.5 }),
       '扇区 21.33N 77.50W');
+    setLocale('ja');
+    assert.equal(hudQuantity(13, 'km'), '13 km');
+    assert.equal(hudQuantity(1.5, 'km', 1), '1.5 km');
     setLocale('en');
     assert.equal(hudQuantity(0, 'km'), '0KM');
     assert.equal(hudQuantity(2069, 'km', 1), '2069.0KM');