diff --git a/mime-node.c b/mime-node.c
index 7363e222..bc41b752 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -151,7 +151,7 @@ set_signature_list_destructor (mime_node_t *node)
 /* Verify a signed mime node (GMime 2.6) */
 static void
 node_verify (mime_node_t *node, GMimeObject *part,
-	     notmuch_crypto_context_t *cryptoctx)
+	     g_mime_3_unused(notmuch_crypto_context_t *cryptoctx))
 {
     GError *err = NULL;
 
@@ -172,7 +172,7 @@ node_verify (mime_node_t *node, GMimeObject *part,
 /* Decrypt and optionally verify an encrypted mime node (GMime 2.6) */
 static void
 node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
-			 notmuch_crypto_context_t *cryptoctx)
+			 g_mime_3_unused(notmuch_crypto_context_t *cryptoctx))
 {
     GError *err = NULL;
     GMimeDecryptResult *decrypt_result = NULL;
diff --git a/util/gmime-extra.h b/util/gmime-extra.h
index 8096dbe3..de275bc1 100644
--- a/util/gmime-extra.h
+++ b/util/gmime-extra.h
@@ -14,6 +14,7 @@ GMimeStream *g_mime_stream_stdout_new(void);
 #define GMIME_ADDRESS_TYPE_BCC GMIME_RECIPIENT_TYPE_BCC
 
 #define g_mime_2_6_unref(obj) g_object_unref (obj)
+#define g_mime_3_unused(arg) arg
 #define g_mime_certificate_get_fpr16(cert) g_mime_certificate_get_key_id (cert)
 #define g_mime_certificate_get_uid(cert) g_mime_certificate_get_name (cert);
 #else /* GMime >= 3.0 */
@@ -56,6 +57,7 @@ typedef GMimeTrust GMimeCertificateTrust;
 #define GMIME_CERTIFICATE_TRUST_ULTIMATE GMIME_TRUST_ULTIMATE
 
 #define g_mime_2_6_unref(obj) /*ignore*/
+#define g_mime_3_unused(arg) unused(arg)
 #endif
 
 /**