diff --git a/app/src/main/java/eu/faircode/email/FragmentCompose.java b/app/src/main/java/eu/faircode/email/FragmentCompose.java
index 2c44e79f43..eb5a1ee94f 100644
--- a/app/src/main/java/eu/faircode/email/FragmentCompose.java
+++ b/app/src/main/java/eu/faircode/email/FragmentCompose.java
@@ -1874,8 +1874,11 @@ public class FragmentCompose extends FragmentBase {
                                     } else if (OpenPgpApi.ACTION_DETACHED_SIGN.equals(data.getAction())) {
                                         name = "signature.asc";
                                         encryption = EntityAttachment.PGP_SIGNATURE;
+                                        String micalg = result.getStringExtra(OpenPgpApi.RESULT_SIGNATURE_MICALG);
+                                        if (TextUtils.isEmpty(micalg))
+                                            throw new IllegalArgumentException("micalg missing");
                                         ct = new ContentType("application/pgp-signature");
-                                        ct.setParameter("micalg", result.getStringExtra(OpenPgpApi.RESULT_SIGNATURE_MICALG));
+                                        ct.setParameter("micalg", micalg);
                                     } else if (OpenPgpApi.ACTION_SIGN_AND_ENCRYPT.equals(data.getAction())) {
                                         name = "encrypted.asc";
                                         encryption = EntityAttachment.PGP_MESSAGE;
diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index 016cae36bb..1962ae874b 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -297,8 +297,11 @@ public class MessageHelper {
 
                         final ContentType cts = new ContentType(attachment.type);
                         String micalg = cts.getParameter("micalg");
+                        if (TextUtils.isEmpty(micalg))
+                            Log.e("PGP micalg missing");
                         ParameterList params = cts.getParameterList();
-                        params.remove("micalg");
+                        if (params != null)
+                            params.remove("micalg");
                         cts.setParameterList(params);
 
                         // Build signature
@@ -378,8 +381,13 @@ public class MessageHelper {
 
                         final ContentType cts = new ContentType(attachment.type);
                         String micalg = cts.getParameter("micalg");
+                        if (TextUtils.isEmpty(micalg)) {
+                            Log.e("S/MIME micalg missing");
+                            micalg = "sha-256";
+                        }
                         ParameterList params = cts.getParameterList();
-                        params.remove("micalg");
+                        if (params != null)
+                            params.remove("micalg");
                         cts.setParameterList(params);
 
                         // Build signature