diff --git a/lib/modules/datasource/docker/index.spec.ts b/lib/modules/datasource/docker/index.spec.ts
index 5ccae2c3af5819..1c2026fc883401 100644
--- a/lib/modules/datasource/docker/index.spec.ts
+++ b/lib/modules/datasource/docker/index.spec.ts
@@ -781,7 +781,8 @@ describe('modules/datasource/docker/index', () => {
     });
 
     it('supports architecture-specific digest in OCI manifests with media type', async () => {
-      const currentDigest = 'some-image-digest';
+      const currentDigest =
+        'sha256:0101010101010101010101010101010101010101010101010101010101010101';
 
       httpMock
         .scope(authUrl)
@@ -855,7 +856,8 @@ describe('modules/datasource/docker/index', () => {
     });
 
     it('supports architecture-specific digest in OCI manifests without media type', async () => {
-      const currentDigest = 'some-image-digest';
+      const currentDigest =
+        'sha256:0101010101010101010101010101010101010101010101010101010101010101';
 
       httpMock
         .scope(authUrl)
@@ -1005,7 +1007,8 @@ describe('modules/datasource/docker/index', () => {
     });
 
     it('handles error while retrieving image config blob', async () => {
-      const currentDigest = 'some-image-digest';
+      const currentDigest =
+        'sha256:0101010101010101010101010101010101010101010101010101010101010101';
 
       httpMock
         .scope(authUrl)
@@ -1058,24 +1061,31 @@ describe('modules/datasource/docker/index', () => {
         .scope(baseUrl)
         .get('/', undefined, { badheaders: ['authorization'] })
         .reply(200, { token: 'some-token' })
-        .head('/library/some-dep/manifests/some-digest')
+        .head(
+          '/library/some-dep/manifests/sha256:0101010101010101010101010101010101010101010101010101010101010101'
+        )
         .reply(404, {});
       httpMock
         .scope(baseUrl)
         .get('/', undefined, { badheaders: ['authorization'] })
         .reply(200, '', {})
-        .head('/library/some-dep/manifests/some-new-value', undefined, {
-          badheaders: ['authorization'],
-        })
+        .head(
+          '/library/some-dep/manifests/sha256:fafafafafafafafafafafafafafafafafafafafafafafafafafafafafafafafa',
+          undefined,
+          {
+            badheaders: ['authorization'],
+          }
+        )
         .reply(401);
 
       const res = await getDigest(
         {
           datasource: 'docker',
           depName: 'some-dep',
-          currentDigest: 'some-digest',
+          currentDigest:
+            'sha256:0101010101010101010101010101010101010101010101010101010101010101',
         },
-        'some-new-value'
+        'sha256:fafafafafafafafafafafafafafafafafafafafafafafafafafafafafafafafa'
       );
       expect(res).toBeNull();
     });
diff --git a/lib/modules/datasource/docker/index.ts b/lib/modules/datasource/docker/index.ts
index 49c98a380288b8..4e8127e60426ae 100644
--- a/lib/modules/datasource/docker/index.ts
+++ b/lib/modules/datasource/docker/index.ts
@@ -22,6 +22,7 @@ import type {
 import { hasKey } from '../../../util/object';
 import { regEx } from '../../../util/regex';
 import { addSecretForSanitizing } from '../../../util/sanitize';
+import { isDockerDigest } from '../../../util/string';
 import {
   ensurePathPrefix,
   ensureTrailingSlash,
@@ -1018,7 +1019,7 @@ export class DockerDatasource extends Datasource {
     let digest: string | null = null;
     try {
       let architecture: string | null | undefined = null;
-      if (currentDigest) {
+      if (currentDigest && isDockerDigest(currentDigest)) {
         architecture = await this.getImageArchitecture(
           registryHost,
           dockerRepository,
diff --git a/lib/util/string.ts b/lib/util/string.ts
index 4b085d07cbe97b..2ef7ae661d3b97 100644
--- a/lib/util/string.ts
+++ b/lib/util/string.ts
@@ -55,3 +55,7 @@ export function looseEquals(
   }
   return a.localeCompare(b, undefined, { sensitivity: 'base' }) === 0;
 }
+
+export function isDockerDigest(input: string): boolean {
+  return /^sha256:[a-f0-9]{64}$/i.test(input);
+}