diff --git a/src/docker-image-digests.test.ts b/src/docker-image-digests.test.ts
index 024cd9df7dc..cf48dfbc8ff 100644
--- a/src/docker-image-digests.test.ts
+++ b/src/docker-image-digests.test.ts
@@ -33,43 +33,67 @@ type DependabotConfig = {
   updates?: DependabotUpdate[];
 };
 
-function resolveFirstFromReference(dockerfile: string): string | undefined {
+function resolveArgDefaults(dockerfile: string): Map<string, string> {
   const argDefaults = new Map<string, string>();
-
   for (const line of dockerfile.split(/\r?\n/)) {
     const trimmed = line.trim();
-    if (!trimmed) {
-      continue;
-    }
-    if (trimmed.startsWith("FROM ")) {
-      break;
-    }
     const argMatch = trimmed.match(/^ARG\s+([A-Z0-9_]+)=(.+)$/);
     if (!argMatch) {
       continue;
     }
     const [, name, rawValue] = argMatch;
-    const value = rawValue.replace(/^["']|["']$/g, "");
-    argDefaults.set(name, value);
-  }
-
-  const fromLine = dockerfile.split(/\r?\n/).find((line) => line.trimStart().startsWith("FROM "));
-  if (!fromLine) {
-    return undefined;
+    argDefaults.set(name, rawValue.replace(/^["']|["']$/g, ""));
   }
+  return argDefaults;
+}
 
+function resolveFromImageRef(fromLine: string, argDefaults: Map<string, string>): string {
   const fromMatch = fromLine.trim().match(/^FROM\s+(\S+?)(?:\s+AS\s+\S+)?$/);
   if (!fromMatch) {
-    return undefined;
+    return fromLine;
   }
   const imageRef = fromMatch[1];
   const argName =
     imageRef.match(/^\$\{([A-Z0-9_]+)\}$/)?.[1] ?? imageRef.match(/^\$([A-Z0-9_]+)$/)?.[1];
-
   if (!argName) {
     return imageRef;
   }
-  return argDefaults.get(argName);
+  return argDefaults.get(argName) ?? imageRef;
+}
+
+function resolveAllArgBackedFromReferences(
+  dockerfile: string,
+): { stage: string; imageRef: string }[] {
+  const argDefaults = resolveArgDefaults(dockerfile);
+  const results: { stage: string; imageRef: string }[] = [];
+  let stageIndex = 0;
+  for (const line of dockerfile.split(/\r?\n/)) {
+    const trimmed = line.trim();
+    if (!trimmed.startsWith("FROM ")) {
+      continue;
+    }
+    const imageRef = resolveFromImageRef(trimmed, argDefaults);
+    // Only check FROM lines that use an ARG — literal `FROM scratch` etc. are intentionally unpinned.
+    const usesArg =
+      trimmed.match(/FROM\s+\$\{[A-Z0-9_]+\}/) !== null ||
+      trimmed.match(/FROM\s+\$[A-Z0-9_]+/) !== null;
+    if (usesArg) {
+      const stageMatch = trimmed.match(/AS\s+(\S+)/i);
+      const stageName = stageMatch ? stageMatch[1] : `stage-${stageIndex}`;
+      results.push({ stage: stageName, imageRef });
+    }
+    stageIndex += 1;
+  }
+  return results;
+}
+
+function resolveFirstFromReference(dockerfile: string): string | undefined {
+  const argDefaults = resolveArgDefaults(dockerfile);
+  const fromLine = dockerfile.split(/\r?\n/).find((line) => line.trimStart().startsWith("FROM "));
+  if (!fromLine) {
+    return undefined;
+  }
+  return resolveFromImageRef(fromLine, argDefaults);
 }
 
 describe("docker base image pinning", () => {
@@ -84,6 +108,18 @@ describe("docker base image pinning", () => {
     }
   });
 
+  it("pins all ARG-backed FROM stages in selected Dockerfiles to sha256 digests", async () => {
+    for (const dockerfilePath of DIGEST_PINNED_DOCKERFILES) {
+      const dockerfile = await readFile(resolve(repoRoot, dockerfilePath), "utf8");
+      const stages = resolveAllArgBackedFromReferences(dockerfile);
+      for (const { stage, imageRef } of stages) {
+        expect(imageRef, `${dockerfilePath} stage "${stage}" must be digest-pinned`).toMatch(
+          /^\S+@sha256:[a-f0-9]{64}$/,
+        );
+      }
+    }
+  });
+
   it("keeps Dependabot Docker updates enabled for root Dockerfiles", async () => {
     const raw = await readFile(resolve(repoRoot, ".github/dependabot.yml"), "utf8");
     const config = parse(raw) as DependabotConfig;