diff --git a/otp.c b/otp.c
index 021803b..05316bc 100644
--- a/otp.c
+++ b/otp.c
@@ -75,9 +75,17 @@ hotp(enum otp_hmac hmac, const void *key, size_t key_len, uint64_t counter,
 		return -1;
 
 	switch (hmac) {
-	case OTP_HMAC_SHA1: evp_md = EVP_sha1(); break;
-	case OTP_HMAC_SHA256: evp_md = EVP_sha256(); break;
-	case OTP_HMAC_SHA512: evp_md = EVP_sha512(); break;
+	case OTP_HMAC_SHA1:
+		evp_md = EVP_sha1();
+		break;
+	case OTP_HMAC_SHA256:
+		evp_md = EVP_sha256();
+		break;
+	case OTP_HMAC_SHA512:
+		evp_md = EVP_sha512();
+		break;
+	default:
+		return -1;
 	}
 
 	return otp(evp_md, key, (int)key_len, counter, digits);