diff --git a/changelog.d/1782-social-size-rollover.fixed.md b/changelog.d/1782-social-size-rollover.fixed.md
new file mode 100644
index 000000000..52e94c773
--- /dev/null
+++ b/changelog.d/1782-social-size-rollover.fixed.md
@@ -0,0 +1 @@
+Bot Social no longer prints `1024.0 KB` for a file just under a megabyte: a size that rounds up to 1024 KB is shown as `1.0 MB` ([#1782](https://github.com/ThinkFlowLab/FlyBot/issues/1782)).
diff --git a/plugins/social/src/social.js b/plugins/social/src/social.js
index 762e2dc13..867bc16f2 100644
--- a/plugins/social/src/social.js
+++ b/plugins/social/src/social.js
@@ -94,7 +94,13 @@ const sha256 = bytes => createHash('sha256').update(bytes).digest('hex')
 const MIME = { '.txt': 'text/plain', '.md': 'text/markdown', '.csv': 'text/csv', '.tsv': 'text/tab-separated-values', '.json': 'application/json', '.pdf': 'application/pdf', '.png': 'image/png', '.jpg': 'image/jpeg', '.jpeg': 'image/jpeg', '.gif': 'image/gif', '.webp': 'image/webp', '.docx': 'application/vnd.openxmlformats-officedocument.wordprocessingml.document', '.xlsx': 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', '.pptx': 'application/vnd.openxmlformats-officedocument.presentationml.presentation' }
 export const mimeOf = name => MIME[extname(String(name)).toLowerCase()] ?? 'application/octet-stream'
 const TEXTUAL = new Set(['text/plain', 'text/markdown', 'text/csv', 'text/tab-separated-values', 'application/json'])
-const sizeLabel = n => (n < 1024 ? `${n} B` : n < 1048576 ? `${(n / 1024).toFixed(1)} KB` : `${(n / 1048576).toFixed(1)} MB`)
+// The unit comes from the rounded KB figure: a size that rounds up to 1024 KB prints as MB,
+// never as "1024.0 KB" (#1782).
+export const sizeLabel = (n) => {
+  if (n < 1024) return `${n} B`
+  const kb = (n / 1024).toFixed(1)
+  return Number(kb) >= 1024 ? `${(n / 1048576).toFixed(1)} MB` : `${kb} KB`
+}
 // Remote strings that reach model-visible text: one line, no brackets or markup, capped.
 export const cleanText = (value, fallback = '') => String(value ?? '').replace(/[\u0000-\u001f\u007f-\u009f\u2028\u2029]/g, ' ').replace(/[[\]"<>`]/g, '').replace(/\s+/g, ' ').trim().slice(0, 60) || fallback
 // Owner-only draft body: keep punctuation the friend will see; strip controls and cap.
diff --git a/plugins/social/test/size-label.test.js b/plugins/social/test/size-label.test.js
new file mode 100644
index 000000000..2249eeedd
--- /dev/null
+++ b/plugins/social/test/size-label.test.js
@@ -0,0 +1,17 @@
+import assert from 'node:assert/strict'
+import { test } from 'node:test'
+import { sizeLabel } from '../src/social.js'
+
+// #1782: just under a MiB the KB branch rounded to "1024.0 KB". The unit is chosen from the
+// rounded KB figure, so a size that rounds to 1024 KB is printed as MB instead.
+test('#1782: a size that rounds to 1024 KB rolls over to MB', () => {
+  assert.equal(sizeLabel(1_048_570), '1.0 MB')
+  assert.equal(sizeLabel(1_048_575), '1.0 MB')
+})
+
+test('#1782: the MB boundary and ordinary sizes keep their unit', () => {
+  assert.equal(sizeLabel(1_048_576), '1.0 MB')
+  assert.equal(sizeLabel(1_048_000), '1023.4 KB')
+  assert.equal(sizeLabel(1023), '1023 B')
+  assert.equal(sizeLabel(3_145_728), '3.0 MB')
+})