diff --git a/lib/rexml/parsers/baseparser.rb b/lib/rexml/parsers/baseparser.rb
index 02759e70..4e34a183 100644
--- a/lib/rexml/parsers/baseparser.rb
+++ b/lib/rexml/parsers/baseparser.rb
@@ -635,7 +635,10 @@ def process_instruction(start_position)
           @source.position = start_position
           raise REXML::ParseException.new(message, @source)
         end
-        if @document_status.nil? and match_data[1] == "xml"
+        if match_data[1] == "xml"
+          if @document_status
+            raise ParseException.new("Malformed XML: XML declaration is not at the start", @source)
+          end
           content = match_data[2]
           version = VERSION.match(content)
           version = version[1] unless version.nil?
diff --git a/test/parse/test_processing_instruction.rb b/test/parse/test_processing_instruction.rb
index f0c0c24e..5e4b1fc9 100644
--- a/test/parse/test_processing_instruction.rb
+++ b/test/parse/test_processing_instruction.rb
@@ -39,6 +39,23 @@ def test_garbage_text
                        pi.content,
                      ])
       end
+
+      def test_xml_declaration_not_at_document_start
+        exception = assert_raise(REXML::ParseException) do
+          parser = REXML::Parsers::BaseParser.new('<a><?xml version="1.0" ?></a>')
+          while parser.has_next?
+            parser.pull
+          end
+        end
+
+        assert_equal(<<~DETAIL.chomp, exception.to_s)
+          Malformed XML: XML declaration is not at the start
+          Line: 1
+          Position: 25
+          Last 80 unconsumed characters:
+
+        DETAIL
+      end
     end
   end
 end