diff --git a/lib/net/imap.rb b/lib/net/imap.rb
index 6bd2f107..397f24b8 100644
--- a/lib/net/imap.rb
+++ b/lib/net/imap.rb
@@ -3151,6 +3151,10 @@ def enforce_logindisabled?
     end
 
     def search_args(keys, charset = nil)
+      # NOTE: not handling combined RETURN and CHARSET for raw strings
+      if charset && keys in /\ACHARSET\b/i | Array[/\ACHARSET\z/i, *]
+        raise ArgumentError, "multiple charset arguments"
+      end
       args = normalize_searching_criteria(keys)
       args.prepend("CHARSET", charset)     if charset
       args
diff --git a/test/net/imap/test_imap.rb b/test/net/imap/test_imap.rb
index 5fa9d643..fc2ccdd5 100644
--- a/test/net/imap/test_imap.rb
+++ b/test/net/imap/test_imap.rb
@@ -1265,6 +1265,24 @@ def seqset_coercible.to_sequence_set
     end
   end
 
+  test("#search/#uid_search with invalid arguments") do
+    with_fake_server do |server, imap|
+      server.on "SEARCH"     do |cmd| cmd.fail_no "should fail before this" end
+      server.on "UID SEARCH" do |cmd| cmd.fail_no "should fail before this" end
+
+      assert_raise(ArgumentError) do
+        imap.search(["charset", "foo", "ALL"], "bar")
+      end
+      assert_raise(ArgumentError) do
+        imap.search("charset foo ALL", "bar")
+      end
+      # Parsing return opts is too complicated, for now.
+      # assert_raise(ArgumentError) do
+      #   imap.search("return () charset foo ALL", "bar")
+      # end
+    end
+  end
+
   test("missing server SEARCH response") do
     with_fake_server do |server, imap|
       server.on "SEARCH",     &:done_ok