diff --git a/commands/policy/eval.go b/commands/policy/eval.go
index 77a84d07e..2d516215c 100644
--- a/commands/policy/eval.go
+++ b/commands/policy/eval.go
@@ -388,6 +388,7 @@ func parseSource(input string) (*pb.SourceOp, error) {
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to parse image source reference")
 		}
+		ref = reference.TagNameOnly(ref)
 		return &pb.SourceOp{Identifier: "docker-image://" + ref.String()}, nil
 	}
 	if strings.HasPrefix(input, "git://") {
diff --git a/policy/signatures.go b/policy/signatures.go
index 5c87b2c2c..daa0178d2 100644
--- a/policy/signatures.go
+++ b/policy/signatures.go
@@ -89,6 +89,10 @@ func parseSignatures(ctx context.Context, getVerifier PolicyVerifierProvider, ac
 	}
 	desc := toOCIDescriptor(rootBlob.Descriptor_)
 
+	if desc.MediaType != ocispecs.MediaTypeImageIndex {
+		return nil, nil
+	}
+
 	sc, err := policyimage.ResolveSignatureChain(ctx, acp, desc, platform)
 	if err != nil {
 		return nil, errors.Wrapf(err, "resolving signature chain for image %s", desc.Digest)