diff --git a/internal/scti/ctlog_test.go b/internal/scti/ctlog_test.go
index 05cac5a2..aaae7f5c 100644
--- a/internal/scti/ctlog_test.go
+++ b/internal/scti/ctlog_test.go
@@ -3,10 +3,18 @@ package scti
 import (
 	"context"
 	"crypto"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"os"
 	"strings"
 	"testing"
 
-	"github.com/google/trillian/crypto/keys/pem"
+	trillianpem "github.com/google/trillian/crypto/keys/pem"
 	"github.com/transparency-dev/static-ct/internal/x509util"
 	"github.com/transparency-dev/static-ct/storage"
 	"golang.org/x/mod/sumdb/note"
@@ -14,10 +22,14 @@ import (
 
 func TestNewLog(t *testing.T) {
 	ctx := context.Background()
-	signer, err := pem.ReadPrivateKeyFile("../testdata/ct-http-server.privkey.pem", "dirk")
+	ecdsaSigner, err := trillianpem.ReadPrivateKeyFile("../testdata/ct-http-server.privkey.pem", "dirk")
 	if err != nil {
 		t.Fatalf("Can't open key: %v", err)
 	}
+	rsaSigner, err := loadPEMPrivateKey("../testdata/test_rsa_private_key.pem")
+	if err != nil {
+		t.Fatalf("Failed to generate RSA key: %v", err)
+	}
 	roots := x509util.NewPEMCertPool()
 	if err := roots.AppendCertsFromPEMFile("../testdata/fake-ca.cert"); err != nil {
 		t.Fatalf("Can't open roots: %v", err)
@@ -34,14 +46,30 @@ func TestNewLog(t *testing.T) {
 			desc:    "empty-origin",
 			wantErr: "empty origin",
 		},
-		// TODO(phboneff): add a test for a signer of the wrong type
+		{
+			desc:   "empty-signer",
+			origin: "testlog",
+			cvOpts: ChainValidationOpts{
+				trustedRoots: roots,
+			},
+			wantErr: "empty signer",
+		},
 		{
 			desc:   "ok",
 			origin: "testlog",
 			cvOpts: ChainValidationOpts{
 				trustedRoots: roots,
 			},
-			signer: signer,
+			signer: ecdsaSigner,
+		},
+		{
+			desc:   "incorrect-signer-type",
+			origin: "testlog",
+			cvOpts: ChainValidationOpts{
+				trustedRoots: roots,
+			},
+			signer:  rsaSigner,
+			wantErr: "unsupported key type",
 		},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
@@ -61,3 +89,44 @@ func TestNewLog(t *testing.T) {
 		})
 	}
 }
+
+func loadPEMPrivateKey(path string) (crypto.Signer, error) {
+	keyBytes, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read key file: %w", err)
+	}
+
+	block, _ := pem.Decode(keyBytes)
+	if block == nil {
+		return nil, errors.New("failed to decode PEM private key")
+	}
+
+	// Fix block type for testing keys.
+	block.Type = strings.ReplaceAll(block.Type, "TEST PRIVATE KEY", "PRIVATE KEY")
+
+	var privateKey any
+	switch block.Type {
+	case "RSA PRIVATE KEY":
+		privateKey, err = x509.ParsePKCS1PrivateKey(block.Bytes)
+	case "EC PRIVATE KEY":
+		privateKey, err = x509.ParseECPrivateKey(block.Bytes)
+	case "PRIVATE KEY":
+		privateKey, err = x509.ParsePKCS8PrivateKey(block.Bytes)
+	default:
+		return nil, fmt.Errorf("unsupported PEM block type: %s", block.Type)
+	}
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse private key: %v", err)
+	}
+
+	switch key := privateKey.(type) {
+	case *rsa.PrivateKey:
+		return key, nil
+	case *ecdsa.PrivateKey:
+		return key, nil
+	case ed25519.PrivateKey:
+		return key, nil
+	default:
+		return nil, errors.New("unsupported private key type")
+	}
+}
diff --git a/internal/testdata/test_rsa_private_key.pem b/internal/testdata/test_rsa_private_key.pem
new file mode 100644
index 00000000..93d6034f
--- /dev/null
+++ b/internal/testdata/test_rsa_private_key.pem
@@ -0,0 +1,27 @@
+-----BEGIN RSA TEST PRIVATE KEY-----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+-----END RSA TEST PRIVATE KEY-----