diff --git a/lib/enmail/helpers/rfc1847.rb b/lib/enmail/helpers/rfc1847.rb
index 9bdc345..94b1996 100644
--- a/lib/enmail/helpers/rfc1847.rb
+++ b/lib/enmail/helpers/rfc1847.rb
@@ -85,7 +85,7 @@ def build_signature_part(signature)
         part
       end
 
-      def multipart_signed_content_type(protocol: sign_protocol, micalg: message_integrity_algorithm)
+      def multipart_signed_content_type(protocol: sign_protocol, micalg:)
         %[multipart/signed; protocol="#{protocol}"; micalg="#{micalg}"]
       end
 
diff --git a/lib/enmail/helpers/rfc3156.rb b/lib/enmail/helpers/rfc3156.rb
index ab2c039..6917ab7 100644
--- a/lib/enmail/helpers/rfc3156.rb
+++ b/lib/enmail/helpers/rfc3156.rb
@@ -51,10 +51,6 @@ def encryption_protocol
         "application/pgp-encrypted"
       end
 
-      def message_integrity_algorithm
-        "pgp-sha1"
-      end
-
       # As defined in RFC 3156
       def encryption_control_information
         "Version: 1"
diff --git a/spec/unit/helpers/rfc1847_spec.rb b/spec/unit/helpers/rfc1847_spec.rb
index 64f5a13..f904abb 100644
--- a/spec/unit/helpers/rfc1847_spec.rb
+++ b/spec/unit/helpers/rfc1847_spec.rb
@@ -273,12 +273,9 @@
       expect(retval_segments[1..-1]).to include(micalg_def)
     end
 
-    it "defaults micalg argument to value returned by " +
-      "#message_integrity_algorithm" do
+    it "requires micalg argument" do
       args.delete :micalg
-      retval_segments = subject.call(args).split(/\s*;\s*/)
-      micalg_def = %[micalg="#{adapter.message_integrity_algorithm}"]
-      expect(retval_segments[1..-1]).to include(micalg_def)
+      expect { subject.call(args) }.to raise_error(ArgumentError)
     end
 
     it "tells about PGP protocol given as argument" do