diff --git a/Bonsai.Editor/DocumentationException.cs b/Bonsai.Editor/DocumentationException.cs
new file mode 100644
index 00000000..4223ef8f
--- /dev/null
+++ b/Bonsai.Editor/DocumentationException.cs
@@ -0,0 +1,19 @@
+using System;
+
+namespace Bonsai.Editor
+{
+    internal sealed class DocumentationException : Exception
+    {
+        public DocumentationException()
+            : base()
+        { }
+
+        public DocumentationException(string message)
+            : base(message)
+        { }
+
+        public DocumentationException(string message, Exception innerException)
+            : base(message, innerException)
+        { }
+    }
+}
diff --git a/Bonsai.Editor/DocumentationHelper.cs b/Bonsai.Editor/DocumentationHelper.cs
index 9de19bc7..92d34bad 100644
--- a/Bonsai.Editor/DocumentationHelper.cs
+++ b/Bonsai.Editor/DocumentationHelper.cs
@@ -5,6 +5,7 @@
 using System.Net;
 using System.Net.Cache;
 using System.Threading.Tasks;
+using YamlDotNet.Core;
 using YamlDotNet.Serialization;
 using YamlDotNet.Serialization.NamingConventions;
 
@@ -36,16 +37,14 @@ static async Task<Dictionary<string, string>> GetXRefMapAsync(string baseUrl, pa
                 throw new ArgumentException("No downstream URLs have been specified.", nameof(hrefs));
             }
 
-            WebException lastException = default;
+            Exception lastException = default;
             for (int i = 0; i < hrefs.Length; i++)
             {
                 try { return await GetXRefMapAsync($"{baseUrl}{hrefs[i]}"); }
-                catch (WebException ex) when (ex.Response is HttpWebResponse httpResponse &&
-                                              httpResponse.StatusCode is HttpStatusCode.NotFound)
-                {
-                    lastException = ex;
-                    continue;
-                }
+                catch (WebException ex) when (ex.Response is HttpWebResponse { StatusCode: HttpStatusCode.NotFound })
+                { lastException ??= ex; } // Always prefer a DocumentationException as it'll be more specific
+                catch (DocumentationException ex)
+                { lastException = ex; }
             }
 
             throw lastException;
@@ -61,11 +60,25 @@ static async Task<Dictionary<string, string>> GetXRefMapAsync(string baseUrl)
             using var response = await request.GetResponseAsync();
             var stream = response.GetResponseStream();
             using var reader = new StreamReader(stream);
+
+            if (reader.ReadLine().Trim() != "### YamlMime:XRefMap")
+                throw new DocumentationException("The documentation server did not respond with a cross-reference map.");
+
             var deserializer = new DeserializerBuilder()
                 .WithNamingConvention(CamelCaseNamingConvention.Instance)
                 .IgnoreUnmatchedProperties()
                 .Build();
-            var xrefmap = deserializer.Deserialize<XRefMap>(reader);
+
+            XRefMap xrefmap;
+            try { xrefmap = deserializer.Deserialize<XRefMap>(reader); }
+            catch (YamlException ex)
+            {
+                throw new DocumentationException("The cross-reference map returned by the documentation server is malformed.", ex);
+            }
+
+            if (xrefmap.References is null)
+                throw new DocumentationException("The cross-reference map returned by the documentation server is malformed.");
+
             return xrefmap.References.ToDictionary(
                 reference => reference.Uid,
                 reference => $"{baseUrl}/{reference.Href}");
diff --git a/Bonsai.Editor/EditorForm.cs b/Bonsai.Editor/EditorForm.cs
index 06f5fa39..bf12a9e4 100644
--- a/Bonsai.Editor/EditorForm.cs
+++ b/Bonsai.Editor/EditorForm.cs
@@ -2366,12 +2366,12 @@ private async Task OpenDocumentationAsync(string assemblyName, string uid)
                 var message = $"The specified operator {uid} was not found in the documentation for {assemblyName}.";
                 editorSite.ShowError(ex, message);
             }
-            catch (SystemException ex) when (ex is WebException || ex is NotSupportedException)
+            catch (Exception ex) when (ex is WebException or NotSupportedException or DocumentationException)
             {
                 var message = $"The documentation for the module {assemblyName} is not available. {{0}}";
                 editorSite.ShowError(ex, message);
             }
-            catch (SystemException ex)
+            catch (Exception ex)
             {
                 editorSite.ShowError(ex);
             }