diff --git a/source/gui/settingsDialogs.py b/source/gui/settingsDialogs.py
index d8df8d1461..71b31e39d4 100644
--- a/source/gui/settingsDialogs.py
+++ b/source/gui/settingsDialogs.py
@@ -999,6 +999,7 @@ def onChangeMirrorURL(self, evt: wx.CommandEvent | wx.KeyEvent):
 			configPath=("update", "serverURL"),
 			helpId="SetURLDialog",
 			urlTransformer=lambda url: f"{url}?versionType=stable",
+			responseValidator=_isResponseUpdateMirrorValid,
 		)
 		ret = changeMirror.ShowModal()
 		if ret == wx.ID_OK:
@@ -5595,3 +5596,18 @@ def _isResponseAddonStoreCacheHash(response: requests.Response) -> bool:
 	# While the NV Access Add-on Store cache hash is a git commit hash as a string, other implementations may use a different format.
 	# Therefore, we only check if the data is a non-empty string.
 	return isinstance(data, str) and bool(data)
+
+
+def _isResponseUpdateMirrorValid(response: requests.Response) -> bool:
+	if not response.ok:
+		return False
+
+	responseContent = response.text
+
+	try:
+		parsedResponse = updateCheck.parseUpdateCheckResponse(responseContent)
+	except Exception as e:
+		log.error(f"Error parsing update mirror response: {e}")
+		return False
+
+	return parsedResponse is not None
diff --git a/source/updateCheck.py b/source/updateCheck.py
index 6207831f2f..8fa47146b9 100644
--- a/source/updateCheck.py
+++ b/source/updateCheck.py
@@ -118,6 +118,27 @@ def getQualifiedDriverClassNameForStats(cls):
 	return "%s (core)" % name
 
 
+def parseUpdateCheckResponse(data: str) -> dict[str, str] | None:
+	"""
+	Parses the update response and returns a dictionary with metadata.
+
+	:param data: The raw server response as a UTF-8 decoded string.
+	:return: A dictionary containing the update metadata, or None if the format is invalid.
+	"""
+	if not data.strip():
+		return None
+
+	metadata = {}
+	for line in data.splitlines():
+		try:
+			key, val = line.split(": ", 1)
+			metadata[key] = val
+		except ValueError:
+			return None  # Invalid format
+
+	return metadata
+
+
 UPDATE_FETCH_TIMEOUT_S = 30  # seconds
 
 
@@ -187,15 +208,10 @@ def checkForUpdate(auto: bool = False) -> Optional[Dict]:
 			raise
 	if res.code != 200:
 		raise RuntimeError("Checking for update failed with code %d" % res.code)
-	info = {}
-	for line in res:
-		# #9819: update description resource returns bytes, so make it Unicode.
-		line = line.decode("utf-8").rstrip()
-		try:
-			key, val = line.split(": ", 1)
-		except ValueError:
-			raise RuntimeError("Error in update check output")
-		info[key] = val
+
+	data = res.text
+	info = parseUpdateCheckResponse(data)
+
 	if not info:
 		return None
 	return info
diff --git a/user_docs/en/changes.md b/user_docs/en/changes.md
index 505f12d674..96e2827f1a 100644
--- a/user_docs/en/changes.md
+++ b/user_docs/en/changes.md
@@ -16,7 +16,7 @@ To use this feature, "allow NVDA to control the volume of other applications" mu
 * NVDA can now report when a link destination points to the current page. (#141, @LeonarddeR, @nvdaes)
 * Added an action in the Add-on Store to cancel the install of add-ons. (#15578, @hwf1324)
 * Added an action in the Add-on Store to retry the installation if the download/installation of an add-on fails. (#17090, @hwf1324)
-* It is now possible to specify mirror URLs to use for NVDA updates and the Add-on Store. (#14974, #17151)
+* It is now possible to specify mirror URLs to use for NVDA updates and the Add-on Store. (#14974, #17151, #17310)
 * The add-ons lists in the Add-on Store can be sorted by columns, including publication date, in ascending and descending order. (#15277, #16681, @nvdaes)
 * When decreasing or increasing the font size in LibreOffice Writer using the corresponding keyboard shortcuts, NVDA announces the new font size. (#6915, @michaelweghorn)
 * When applying the "Body Text" or a heading paragraph style using the corresponding keyboard shortcut in LibreOffice Writer 25.2 or newer, NVDA announces the new paragraph style. (#6915, @michaelweghorn)