diff --git a/lib/entry-points.js b/lib/entry-points.js
index 347343d0ed..14c662839a 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -147779,13 +147779,16 @@ function flushDiagnostics(config) {
   unwrittenDiagnostics = [];
   unwrittenDefaultLanguageDiagnostics = [];
 }
-function makeTelemetryDiagnostic(id, name, attributes) {
+function makeTelemetryDiagnostic(id, name, attributes, tags) {
   return makeDiagnostic(id, name, {
     attributes,
     visibility: {
       cliSummaryTable: false,
       statusPage: false,
       telemetry: true
+    },
+    source: {
+      tags
     }
   });
 }
@@ -147987,7 +147990,8 @@ function mergeDefaultSetupAndUserConfigs(logger, fromConfigInput, fromConfigFile
         "Invalid Default Setup configuration keys",
         {
           invalidKeys: schemaCheckResult.invalidKeys
-        }
+        },
+        ["internal-error"]
       )
     );
   }
@@ -148002,7 +148006,8 @@ function mergeDefaultSetupAndUserConfigs(logger, fromConfigInput, fromConfigFile
         "Unrecognised Default Setup configuration keys",
         {
           unrecognisedKeys: schemaCheckResult.unknownKeys
-        }
+        },
+        ["internal-error"]
       )
     );
   }
diff --git a/src/config/db-config.ts b/src/config/db-config.ts
index 582cfe8afc..7b5bdbd8ce 100644
--- a/src/config/db-config.ts
+++ b/src/config/db-config.ts
@@ -125,6 +125,7 @@ export function mergeDefaultSetupAndUserConfigs(
         {
           invalidKeys: schemaCheckResult.invalidKeys,
         },
+        ["internal-error"],
       ),
     );
   }
@@ -140,6 +141,7 @@ export function mergeDefaultSetupAndUserConfigs(
         {
           unrecognisedKeys: schemaCheckResult.unknownKeys,
         },
+        ["internal-error"],
       ),
     );
   }
diff --git a/src/diagnostics.ts b/src/diagnostics.ts
index 65e82ce1af..fa0e87c046 100644
--- a/src/diagnostics.ts
+++ b/src/diagnostics.ts
@@ -6,24 +6,45 @@ import { Language } from "./languages";
 import { getActionsLogger } from "./logging";
 import { getCodeQLDatabasePath } from "./util";
 
-/** Represents a diagnostic message for the tool status page, etc. */
-export interface DiagnosticMessage {
+/**
+ * Known tags for diagnostics. There is currently only "internal-error",
+ * but others may be added in the future.
+ */
+export type DiagnosticTag = "internal-error";
+
+/** Optional information about the origin of a diagnostic. */
+export type DiagnosticSourceOptions = {
+  /**
+   * Name of the CodeQL extractor. This is used to identify which tool component the reporting
+   * descriptor object should be nested under in SARIF.
+   */
+  extractorName?: string;
+  /** An array of tags for the diagnostic. */
+  tags?: DiagnosticTag[];
+};
+
+/** Represents information about the origin of a diagnostic. */
+export type DiagnosticSource = {
+  /**
+   * An identifier under which it makes sense to group this diagnostic message.
+   * This is used to build the SARIF reporting descriptor object.
+   */
+  id: string;
+  /** Display name for the ID. This is used to build the SARIF reporting descriptor object. */
+  name: string;
+} & DiagnosticSourceOptions;
+
+/**
+ * Represents a diagnostic message for the tool status page, etc.
+ *
+ * Unlike {@link DiagnosticMessage}, properties which can automatically
+ * be populated are optional in this type.
+ */
+export type DiagnosticMessageOptions = {
   /** ISO 8601 timestamp */
-  timestamp: string;
-  source: {
-    /**
-     * An identifier under which it makes sense to group this diagnostic message.
-     * This is used to build the SARIF reporting descriptor object.
-     */
-    id: string;
-    /** Display name for the ID. This is used to build the SARIF reporting descriptor object. */
-    name: string;
-    /**
-     * Name of the CodeQL extractor. This is used to identify which tool component the reporting
-     * descriptor object should be nested under in SARIF.
-     */
-    extractorName?: string;
-  };
+  timestamp?: string;
+  /** Information about the origin of the diagnostic. */
+  source?: DiagnosticSourceOptions;
   /** GitHub flavored Markdown formatted message. Should include inline links to any help pages. */
   markdownMessage?: string;
   /** Plain text message. Used by components where the string processing needed to support Markdown is cumbersome. */
@@ -53,7 +74,15 @@ export interface DiagnosticMessage {
   };
   /** Structured metadata about the diagnostic message */
   attributes?: { [key: string]: any };
-}
+};
+
+/** Represents a diagnostic message for the tool status page, etc. */
+export type DiagnosticMessage = DiagnosticMessageOptions & {
+  /** ISO 8601 timestamp */
+  timestamp: string;
+  /** Information about the origin of the diagnostic. */
+  source: DiagnosticSource;
+};
 
 /** Represents a diagnostic message that has not yet been written to the database. */
 interface UnwrittenDiagnostic {
@@ -90,7 +119,7 @@ let diagnosticCounter = 0;
 export function makeDiagnostic(
   id: string,
   name: string,
-  data: Partial<DiagnosticMessage> | undefined = undefined,
+  data: DiagnosticMessageOptions | undefined = undefined,
 ): DiagnosticMessage {
   return {
     ...data,
@@ -243,6 +272,7 @@ export function makeTelemetryDiagnostic(
   id: string,
   name: string,
   attributes: { [key: string]: any },
+  tags?: DiagnosticTag[],
 ): DiagnosticMessage {
   return makeDiagnostic(id, name, {
     attributes,
@@ -251,5 +281,8 @@ export function makeTelemetryDiagnostic(
       statusPage: false,
       telemetry: true,
     },
+    source: {
+      tags,
+    },
   });
 }