diff --git a/lib/entry-points.js b/lib/entry-points.js
index 7561480c4..8b4514637 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -177370,7 +177370,7 @@ async function getCodeQLForCmd(logger2, cmd, checkVersion) {
       }
       await new toolrunner3.ToolRunner(cmd, args).exec();
     },
-    async diagnosticsExport(sarifFile, automationDetailsId, config) {
+    async diagnosticsExport(sarifFile, automationDetailsId, config, diagnosticDir) {
       const args = [
         "diagnostics",
         "export",
@@ -177379,6 +177379,7 @@ async function getCodeQLForCmd(logger2, cmd, checkVersion) {
         `--sarif-codescanning-config=${getGeneratedCodeScanningConfigPath(
           config
         )}`,
+        ...diagnosticDir !== void 0 ? [`--diagnostic-dir=${diagnosticDir}`] : [],
         ...getExtraOptionsFromEnv(["diagnostics", "export"])
       ];
       if (automationDetailsId !== void 0) {
@@ -186909,7 +186910,13 @@ async function generateFailedSarif(logger2, features, config, category, checkout
     sarifFile = "../codeql-failed-run.sarif";
   }
   if (databasePath === void 0 || !await features.getValue("export_diagnostics_enabled" /* ExportDiagnosticsEnabled */, codeql)) {
-    await codeql.diagnosticsExport(sarifFile, category, config);
+    let diagnosticDir = getTempDiagnosticPath(
+      config.tempDir
+    );
+    if (!fs31.existsSync(diagnosticDir)) {
+      diagnosticDir = void 0;
+    }
+    await codeql.diagnosticsExport(sarifFile, category, config, diagnosticDir);
   } else {
     await codeql.databaseExportDiagnostics(databasePath, sarifFile, category);
   }
diff --git a/src/codeql.ts b/src/codeql.ts
index 68273d27b..6a0440321 100644
--- a/src/codeql.ts
+++ b/src/codeql.ts
@@ -199,6 +199,7 @@ export interface CodeQL {
     sarifFile: string,
     automationDetailsId: string | undefined,
     config: ActionConfig<"tempDir">,
+    diagnosticDir: string | undefined,
   ): Promise<void>;
   /** Get the location of an extractor for the specified language. */
   resolveExtractor(language: Language): Promise<string>;
@@ -915,6 +916,7 @@ async function getCodeQLForCmd(
       sarifFile: string,
       automationDetailsId: string | undefined,
       config: ActionConfig<"tempDir">,
+      diagnosticDir: string | undefined,
     ): Promise<void> {
       const args = [
         "diagnostics",
@@ -924,6 +926,9 @@ async function getCodeQLForCmd(
         `--sarif-codescanning-config=${getGeneratedCodeScanningConfigPath(
           config,
         )}`,
+        ...(diagnosticDir !== undefined
+          ? [`--diagnostic-dir=${diagnosticDir}`]
+          : []),
         ...getExtraOptionsFromEnv(["diagnostics", "export"]),
       ];
       if (automationDetailsId !== undefined) {
diff --git a/src/init-action-post-helper.ts b/src/init-action-post-helper.ts
index b6aeb5bd3..3d736f9d5 100644
--- a/src/init-action-post-helper.ts
+++ b/src/init-action-post-helper.ts
@@ -24,6 +24,7 @@ import {
   type UploadDebugArtifactsConfig,
 } from "./debug-artifacts";
 import * as dependencyCaching from "./dependency-caching";
+import { getTempDiagnosticPath } from "./diagnostics";
 import { EnvVar, ReadOnlyEnv } from "./environment";
 import { Feature, FeatureEnablement } from "./feature-flags";
 import { Logger } from "./logging";
@@ -189,7 +190,19 @@ async function generateFailedSarif(
     databasePath === undefined ||
     !(await features.getValue(Feature.ExportDiagnosticsEnabled, codeql))
   ) {
-    await codeql.diagnosticsExport(sarifFile, category, config);
+    // If we don't have a database path, then we may have diagnostics that were written to a
+    // temporary location. Get the path that they would have been written to and check whether
+    // it exists. If so, pass it on to the CLI. The CLI will not complain if we give it a
+    // path that doesn't exist, so we are just being extra defensive here.
+    let diagnosticDir: string | undefined = getTempDiagnosticPath(
+      config.tempDir,
+    );
+
+    if (!fs.existsSync(diagnosticDir)) {
+      diagnosticDir = undefined;
+    }
+
+    await codeql.diagnosticsExport(sarifFile, category, config, diagnosticDir);
   } else {
     // We call 'database export-diagnostics' to find any per-database diagnostics.
     await codeql.databaseExportDiagnostics(databasePath, sarifFile, category);