diff --git a/src/POI/PresetValueTextField.swift b/src/POI/PresetValueTextField.swift
index 9cb850773..1c251e85b 100644
--- a/src/POI/PresetValueTextField.swift
+++ b/src/POI/PresetValueTextField.swift
@@ -200,7 +200,8 @@ class PresetValueTextField: AutocompleteTextField, PanoramaxDelegate {
 
 	private func updateAssociatedContent() {
 		// Swift doesn't like too many ??'s so we break it into pieces 🤷‍♂️
-		let associatedView1 = getSurveyDateButton()
+		let associatedView1 = getFormatWarningButton()
+		    ?? getSurveyDateButton()
 			?? getAssociatedColor()
 			?? getOpeningHoursButton()
 			?? getWebsiteButton()
@@ -219,6 +220,47 @@ class PresetValueTextField: AutocompleteTextField, PanoramaxDelegate {
 		}
 	}
 
+	// MARK: Value format warning
+
+	private func getFormatWarningButton() -> UIView? {
+		guard key != "",
+		      let value = text,
+		      value != "",
+		      let regex = WikiPage.shared.valueFormat(forKey: key, update: { [weak self] in
+		      	self?.updateAssociatedContent()
+		      }),
+		      !WikiPage.value(value, matches: regex)
+		else { return nil }
+		let button = UIButton(type: .system)
+		button.setImage(UIImage(systemName: "exclamationmark.triangle.fill"), for: .normal)
+		button.tintColor = .systemOrange
+		button.accessibilityLabel = NSLocalizedString("Unexpected format", comment: "")
+		button.addTarget(self, action: #selector(showFormatWarning), for: .touchUpInside)
+		return button
+	}
+
+	@objc private func showFormatWarning() {
+		guard let viewController = owner.viewController,
+		      let regex = WikiPage.shared.valueFormat(forKey: key, update: {})
+		else { return }
+		let message = String.localizedStringWithFormat(
+			NSLocalizedString("The OpenStreetMap Wiki says values for %@ should match this pattern:\n\n%@",
+			                  comment: "tag key, regular expression"),
+			key,
+			String(regex.pattern.dropFirst(4).dropLast(2)))
+		let alert = UIAlertController(title: NSLocalizedString("Unexpected Format", comment: ""),
+		                              message: message,
+		                              preferredStyle: .alert)
+		alert.addAction(UIAlertAction(title: NSLocalizedString("OK", comment: ""), style: .cancel))
+		alert.addAction(UIAlertAction(title: NSLocalizedString("Read more on the Wiki", comment: ""),
+		                              style: .default)
+		{ [key] _ in
+			let url = WikiPage.shared.urlFor(pageTitle: "Key:" + key)
+			viewController.present(SFSafariViewController(url: url), animated: true)
+		})
+		viewController.present(alert, animated: true)
+	}
+	
 	// MARK: Color preview
 
 	private func getAssociatedColor() -> UIView? {
diff --git a/src/Shared/Utility/WikiPage.swift b/src/Shared/Utility/WikiPage.swift
index f92df79aa..5fd28a445 100644
--- a/src/Shared/Utility/WikiPage.swift
+++ b/src/Shared/Utility/WikiPage.swift
@@ -163,10 +163,58 @@ class WikiPage {
 	private let imageCache = PersistentWebCache<UIImage>(name: "wikiImageStore",
 	                                                     memorySize: 10_000000,
 	                                                     daysToKeep: 14.0)
+	private class ValueFormat {
+		let regex: NSRegularExpression?
 
+		init(regex: NSRegularExpression?) {
+			self.regex = regex
+		}
+	}
+
+	private let valueFormatCache = PersistentWebCache<ValueFormat>(name: "wikiValueFormatStore",
+	                                                               memorySize: 1_000000,
+	                                                               daysToKeep: 14.0)
+	
 	func resetCache() {
 		descriptionCache.removeAllObjects()
 		imageCache.removeAllObjects()
+		valueFormatCache.removeAllObjects()
+	}
+
+	func valueFormat(forKey key: String, update: @escaping () -> Void) -> NSRegularExpression? {
+		return valueFormatCache.object(
+			withKey: key,
+			fallbackURL: {
+				var comps = URLComponents(string: "https://wiki.openstreetmap.org/w/api.php")!
+				comps.queryItems = [
+					URLQueryItem(name: "action", value: "wbgetentities"),
+					URLQueryItem(name: "sites", value: "wiki"),
+					URLQueryItem(name: "titles", value: "Key:" + key.replacingOccurrences(of: "_", with: " ")),
+					URLQueryItem(name: "props", value: "claims|sitelinks"),
+					URLQueryItem(name: "format", value: "json")
+				]
+				return comps.url
+			},
+			objectForData: { data in
+				guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
+				      let entities = json["entities"] as? [String: Any]
+				else { return nil }
+				guard let entity = self.entity(in: entities, withTitlePrefix: "Key:"),
+				      let pattern = self.valueFor(property: "P13", inEntity: entity, langQID: "")
+				else { return ValueFormat(regex: nil) }
+				return ValueFormat(regex: try? NSRegularExpression(pattern: "^(?:\(pattern))$"))
+			},
+			completion: { result in
+				if (try? result.get())?.regex != nil {
+					update()
+				}
+			})?.regex
+	}
+
+	static func value(_ value: String, matches regex: NSRegularExpression) -> Bool {
+		func matches(_ text: String) -> Bool {
+			return regex.firstMatch(in: text, range: NSRange(text.startIndex..., in: text)) != nil
+		}
 	}
 
 	private func propertyListFor(property: String, inEntity entity: [String: Any]) -> [[String: Any]]? {