diff --git a/src/__tests__/MindMap.spec.js b/src/__tests__/MindMap.spec.js
index 507ef3fc..f40f259f 100644
--- a/src/__tests__/MindMap.spec.js
+++ b/src/__tests__/MindMap.spec.js
@@ -49,6 +49,13 @@ function mountMindMap(dataOverrides = {}) {
 	})
 }
 
+/**
+ * Mount into the document, so the iframe has a window to talk to.
+ */
+function mountAttached() {
+	return shallowMount(MindMap, { attachTo: document.body, global: { mixins: [viewerMixin] } })
+}
+
 describe('MindMap', () => {
 	beforeEach(() => {
 		window.OCA = { FilesMindMap: { setFile: vi.fn() } }
@@ -105,4 +112,44 @@ describe('MindMap', () => {
 			expect(window.OCA.FilesMindMap.setFile).toHaveBeenCalled()
 		})
 	})
+
+	describe('Ctrl+S', () => {
+		it('saves the mind map instead of the browser saving the page', () => {
+			const wrapper = mountAttached()
+			const save = vi.fn()
+			wrapper.element.contentWindow.MindMap = { save }
+
+			const event = new KeyboardEvent('keydown', { key: 's', ctrlKey: true, cancelable: true })
+			document.dispatchEvent(event)
+
+			expect(save).toHaveBeenCalledOnce()
+			expect(event.defaultPrevented).toBe(true)
+			wrapper.unmount()
+		})
+
+		it('leaves other keys alone', () => {
+			const wrapper = mountAttached()
+			const save = vi.fn()
+			wrapper.element.contentWindow.MindMap = { save }
+
+			const event = new KeyboardEvent('keydown', { key: 's', cancelable: true })
+			document.dispatchEvent(event)
+
+			expect(save).not.toHaveBeenCalled()
+			expect(event.defaultPrevented).toBe(false)
+			wrapper.unmount()
+		})
+
+		it('stops handling Ctrl+S once the viewer closes', () => {
+			const add = vi.spyOn(document, 'addEventListener')
+			const remove = vi.spyOn(document, 'removeEventListener')
+			const wrapper = mountAttached()
+			const [, handler] = add.mock.calls.find(([type]) => type === 'keydown')
+			wrapper.unmount()
+
+			expect(remove).toHaveBeenCalledWith('keydown', handler)
+			add.mockRestore()
+			remove.mockRestore()
+		})
+	})
 })
diff --git a/src/__tests__/mindmap.spec.js b/src/__tests__/mindmap.spec.js
index e0173758..249bb308 100644
--- a/src/__tests__/mindmap.spec.js
+++ b/src/__tests__/mindmap.spec.js
@@ -214,6 +214,12 @@ describe('FilesMindMap', () => {
 			FilesMindMap.setFile({ filename: '/docs/sub/test.km', basename: 'test.km' })
 			expect(FilesMindMap._currentContext).toEqual(expect.objectContaining({ dir: '/docs/sub' }))
 		})
+
+		it('forgets the previous file when the viewer passes none', () => {
+			FilesMindMap.setFile({ filename: '/docs/test.km', basename: 'test.km' })
+			expect(() => FilesMindMap.setFile(undefined)).not.toThrow()
+			expect(FilesMindMap._file).toEqual({})
+		})
 	})
 
 	// ─── Public share detection ────────────────────────────────────────────────
diff --git a/src/mindmap.js b/src/mindmap.js
index 65466c55..e769e062 100644
--- a/src/mindmap.js
+++ b/src/mindmap.js
@@ -215,6 +215,12 @@ const FilesMindMap = {
 	},
 
 	setFile(file) {
+		// Forget the previous file, so the editor cannot load or save it in place of this one
+		if (!file) {
+			logger.warn('The viewer passed no file to open')
+			this._file = {}
+			return
+		}
 		const filename = file.filename + ''
 		const basename = file.basename + ''
 
diff --git a/src/viewer.js b/src/viewer.js
index f701c34a..46108aa0 100644
--- a/src/viewer.js
+++ b/src/viewer.js
@@ -110,6 +110,8 @@ normalizeMouseWheel();
 
 	const MindMap = {
 		_changed: false,
+		_saving: false,
+		_saveQueue: [],
 		_autoSaveTimer: null,
 		_clearStatusMessageTimer: null,
 		_loadStatus: false,
@@ -152,13 +154,14 @@ normalizeMouseWheel();
 		},
 		initHotkey() {
 			const self = this
-			window.$(document).keydown(function(e) {
-				if ((e.ctrlKey || e.metaKey) && e.which === 83) {
-					self.save()
+			// Capture phase, so the editor's own key handlers cannot swallow it
+			document.addEventListener('keydown', function(e) {
+				if ((e.ctrlKey || e.metaKey) && e.key.toLowerCase() === 's') {
 					e.preventDefault()
-					return false
+					e.stopPropagation()
+					self.save()
 				}
-			})
+			}, true)
 		},
 		bindEvent() {
 			const self = this
@@ -224,25 +227,55 @@ normalizeMouseWheel();
 		},
 		save(onComplete) {
 			const self = this
-			if (self._changed) {
-				self.updateSaveButtonInfo(t('files_mindmap', 'Saving…'))
-				const data = JSON.stringify(minder.exportJson())
-				window.parent.OCA.FilesMindMap.save(data, function(msg) {
-					self.updateSaveButtonInfo(msg)
-					self._changed = false
-					self.restoreSaveButtonInfo(3000)
-					if (undefined !== onComplete) {
-						onComplete(true, msg)
-					}
-				}, function(msg) {
-					self.updateSaveButtonInfo(msg)
-					self.restoreSaveButtonInfo(3000)
-					if (undefined !== onComplete) {
-						onComplete(false, msg)
-					}
-				})
-				self.restoreSaveButtonInfo(6000)
+			// A second request before the first one returns would fail the server's mtime check
+			if (self._saving) {
+				self._saveQueue.push(onComplete)
+				return
+			}
+			if (!self._changed) {
+				if (undefined !== onComplete) {
+					onComplete(true)
+				}
+				return
+			}
+			const finish = function(status, msg) {
+				self._saving = false
+				if (undefined !== onComplete) {
+					onComplete(status, msg)
+				}
+				const queued = self._saveQueue.splice(0)
+				const notify = function(queuedStatus, queuedMsg) {
+					queued.forEach(function(callback) {
+						if (undefined !== callback) {
+							callback(queuedStatus, queuedMsg)
+						}
+					})
+				}
+				if (queued.length === 0) {
+					return
+				}
+				if (status) {
+					self.save(notify)
+				} else {
+					notify(false, msg)
+				}
 			}
+			self._saving = true
+			// Edits made while the request is out mark the map as changed again
+			self._changed = false
+			self.updateSaveButtonInfo(t('files_mindmap', 'Saving…'))
+			const data = JSON.stringify(minder.exportJson())
+			window.parent.OCA.FilesMindMap.save(data, function(msg) {
+				self.updateSaveButtonInfo(msg)
+				self.restoreSaveButtonInfo(3000)
+				finish(true, msg)
+			}, function(msg) {
+				self._changed = true
+				self.updateSaveButtonInfo(msg)
+				self.restoreSaveButtonInfo(3000)
+				finish(false, msg)
+			})
+			self.restoreSaveButtonInfo(6000)
 		},
 		startAutoSaveTimer() {
 			const self = this
diff --git a/src/views/MindMap.js b/src/views/MindMap.js
index b314c218..3da217d5 100644
--- a/src/views/MindMap.js
+++ b/src/views/MindMap.js
@@ -39,9 +39,34 @@ export default {
 		if (OCA.FilesMindMap) {
 			OCA.FilesMindMap.setFile(this.file)
 		}
+		document.addEventListener('keydown', this.onKeyDown)
 		this.doneLoading()
 	},
 
+	// Vue 2.7 (viewer app) calls beforeDestroy; Vue 3 (test env) calls beforeUnmount.
+	beforeDestroy() {
+		document.removeEventListener('keydown', this.onKeyDown)
+	},
+
+	beforeUnmount() {
+		document.removeEventListener('keydown', this.onKeyDown)
+	},
+
+	methods: {
+		/**
+		 * Save the mind map on Ctrl+S while the focus is outside the editor iframe,
+		 * instead of the browser saving the page.
+		 *
+		 * @param {KeyboardEvent} event the key event
+		 */
+		onKeyDown(event) {
+			if ((event.ctrlKey || event.metaKey) && event.key.toLowerCase() === 's') {
+				event.preventDefault()
+				this.$el.contentWindow?.MindMap?.save()
+			}
+		},
+	},
+
 	render(h) {
 		// Vue 2.7 passes h as an argument; Vue 3 (test env) does not — fall back to the peer dep import.
 		const createElement = typeof h === 'function' ? h : _h