diff --git a/lib/net/imap/response_parser.rb b/lib/net/imap/response_parser.rb
index e9775c00..04e2ee2b 100644
--- a/lib/net/imap/response_parser.rb
+++ b/lib/net/imap/response_parser.rb
@@ -8,6 +8,8 @@ class IMAP < Protocol
 
     # Parses an \IMAP server response.
     class ResponseParser
+      MAX_UID_SET_SIZE = 10_000
+
       include ParserUtils
       extend  ParserUtils::Generator
 
@@ -1889,9 +1891,16 @@ def CopyUID(...)   DeprecatedUIDPlus(...) || CopyUIDData.new(...)   end
       # TODO: remove this code in the v0.6.0 release
       def DeprecatedUIDPlus(validity, src_uids = nil, dst_uids)
         return unless config.parser_use_deprecated_uidplus_data
-        src_uids &&= src_uids.each_ordered_number.to_a
-        dst_uids   = dst_uids.each_ordered_number.to_a
-        UIDPlusData.new(validity, src_uids, dst_uids)
+        compact_uid_sets = [src_uids, dst_uids].compact
+        count = compact_uid_sets.map { _1.count_with_duplicates }.max
+        max   = MAX_UID_SET_SIZE
+        if count <= max
+          src_uids &&= src_uids.each_ordered_number.to_a
+          dst_uids   = dst_uids.each_ordered_number.to_a
+          UIDPlusData.new(validity, src_uids, dst_uids)
+        else
+          parse_error("uid-set is too large: %d > %d", count, max)
+        end
       end
 
       ADDRESS_REGEXP = /\G
diff --git a/test/net/imap/test_imap_response_parser.rb b/test/net/imap/test_imap_response_parser.rb
index e85b0b4e..695f21b9 100644
--- a/test/net/imap/test_imap_response_parser.rb
+++ b/test/net/imap/test_imap_response_parser.rb
@@ -206,6 +206,11 @@ def test_fetch_binary_and_binary_size
     parser = Net::IMAP::ResponseParser.new(config: {
       parser_use_deprecated_uidplus_data:      true,
     })
+    assert_raise_with_message Net::IMAP::ResponseParseError, /uid-set is too large/ do
+      parser.parse(
+        "A004 OK [APPENDUID 1 10000:20000,1] Done\r\n"
+      )
+    end
     response = parser.parse("A004 OK [APPENDUID 1 101:200] Done\r\n")
     uidplus  = response.data.code.data
     assert_instance_of Net::IMAP::UIDPlusData, uidplus
@@ -254,6 +259,11 @@ def test_fetch_binary_and_binary_size
     parser = Net::IMAP::ResponseParser.new(config: {
       parser_use_deprecated_uidplus_data:      true,
     })
+    assert_raise_with_message Net::IMAP::ResponseParseError, /uid-set is too large/ do
+      parser.parse(
+        "A004 OK [copyUID 1 10000:20000,1 1:10001] Done\r\n"
+      )
+    end
     response = parser.parse("A004 OK [copyUID 1 101:200 1:100] Done\r\n")
     uidplus  = response.data.code.data
     assert_instance_of Net::IMAP::UIDPlusData, uidplus