diff --git a/src/models/contact.js b/src/models/contact.js
index 325b641c8f..a1d7017353 100644
--- a/src/models/contact.js
+++ b/src/models/contact.js
@@ -22,6 +22,33 @@ function isEmpty(value) {
 	return (Array.isArray(value) && value.join('') === '') || (!Array.isArray(value) && value === '')
 }
 
+/**
+ * Detect the image type from the magic bytes of base64 encoded image data
+ *
+ * @param {string} photoB64Data the base64 encoded image data
+ * @return {string} the image type, jpeg if unknown
+ */
+function detectImageType(photoB64Data) {
+	// base64 encodings of the magic bytes of the common image formats
+	const signatures = {
+		'/9j/': 'jpeg',
+		iVBOR: 'png',
+		R0lGO: 'gif',
+		UklGR: 'webp',
+		Qk: 'bmp',
+		PHN2Z: 'svg+xml', // '<svg'
+		PD94b: 'svg+xml', // '<?xml'
+	}
+	const signature = Object.keys(signatures).find((signature) => photoB64Data.startsWith(signature))
+	if (!signature) {
+		// browsers detect raster images in an img element from the content,
+		// so an assumed subtype still renders fine, but warn about the guess
+		console.warn('Could not detect the photo type from its content, assuming JPEG')
+		return 'jpeg'
+	}
+	return signatures[signature]
+}
+
 export const ContactKindProperties = ['KIND', 'X-ADDRESSBOOKSERVER-KIND']
 
 export const MinimalContactProperties = [
@@ -271,13 +298,19 @@ export default class Contact {
 			photoType = photoB64.split(';')[0].split('/').pop()
 		}
 
+		// The TYPE parameter is optional (e.g. `PHOTO;ENCODING=b:…`),
+		// so fall back to the magic bytes of the image data (see issue #5401)
+		if (!photoType) {
+			photoType = detectImageType(photoB64Data)
+		}
+
 		// Verify if SVG is valid
 		if (photoType.toLowerCase().startsWith('svg')) {
 			const imageSvg = atob(photoB64Data)
 			const cleanSvg = await sanitizeSVG(imageSvg)
 
 			if (!cleanSvg) {
-				console.error('Invalid SVG for the following contact. Ignoring...', this.contact, { photoB64, photoType })
+				console.error('Invalid SVG for the following contact. Ignoring...', this, { photoB64, photoType })
 				return false
 			}
 		}
@@ -287,7 +320,7 @@ export default class Contact {
 			const blob = b64toBlob(photoB64Data, `image/${photoType}`)
 			return URL.createObjectURL(blob)
 		} catch {
-			console.error('Invalid photo for the following contact. Ignoring...', this.contact, { photoB64, photoType })
+			console.error('Invalid photo for the following contact. Ignoring...', this, { photoB64, photoType })
 			return false
 		}
 	}
diff --git a/tests/javascript/models/contact.test.js b/tests/javascript/models/contact.test.js
index c4c429e46a..45b9a0ea4e 100644
--- a/tests/javascript/models/contact.test.js
+++ b/tests/javascript/models/contact.test.js
@@ -9,6 +9,61 @@ const getPropertyLines = (property, vcard) => {
 	return vcard.match(new RegExp(`^${property}[;:].*`, 'gmi'))
 }
 
+describe('Test getPhotoUrl', () => {
+
+	// 1x1 transparent PNG
+	const pngB64 = 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg=='
+
+	const buildContact = (photoLine, version = '3.0') => new Contact(`
+		BEGIN:VCARD
+		VERSION:${version}
+		UID:123456789-123465-123456-123456789
+		FN:Test contact
+		${photoLine}
+		END:VCARD`.replace(/\t/gmi, ''),
+	{ id: 'addressbook1' })
+
+	beforeAll(() => {
+		global.URL.createObjectURL = jest.fn((blob) => `blob:${blob.type}`)
+	})
+
+	test('photo with an explicit TYPE parameter', async () => {
+		const contact = buildContact(`PHOTO;ENCODING=b;TYPE=png:${pngB64}`)
+
+		expect(await contact.getPhotoUrl()).toStrictEqual('blob:image/png')
+	})
+
+	test('photo without a TYPE parameter is detected from the image data (issue #5401)', async () => {
+		const contact = buildContact(`PHOTO;ENCODING=b:${pngB64}`)
+
+		expect(await contact.getPhotoUrl()).toStrictEqual('blob:image/png')
+	})
+
+	test('jpeg photo without a TYPE parameter', async () => {
+		const contact = buildContact('PHOTO;ENCODING=b:/9j/4AAQSkZJRgABAQ==')
+
+		expect(await contact.getPhotoUrl()).toStrictEqual('blob:image/jpeg')
+	})
+
+	test('photo of an unknown type falls back to jpeg and warns', async () => {
+		const warn = jest.spyOn(console, 'warn').mockImplementation(() => {})
+		// base64 that matches none of the known magic byte signatures
+		const contact = buildContact('PHOTO;ENCODING=b:Zm9vYmFyYmF6cXV4')
+
+		expect(await contact.getPhotoUrl()).toStrictEqual('blob:image/jpeg')
+		expect(warn).toHaveBeenCalled()
+
+		warn.mockRestore()
+	})
+
+	test('photo from a data uri (vCard 4.0)', async () => {
+		const contact = buildContact(`PHOTO:data:image/png;base64,${pngB64}`, '4.0')
+
+		expect(await contact.getPhotoUrl()).toStrictEqual('blob:image/png')
+	})
+
+})
+
 describe('Test stripping quotes from TYPE', () => {
 
 	let contact