diff --git a/lib/redmine/wiki_formatting/markdown/formatter.rb b/lib/redmine/wiki_formatting/markdown/formatter.rb
index 9d1637125..418ab8b14 100644
--- a/lib/redmine/wiki_formatting/markdown/formatter.rb
+++ b/lib/redmine/wiki_formatting/markdown/formatter.rb
@@ -89,7 +89,7 @@ module Redmine
           i = 0
           l = 1
           inside_pre = false
-          @text.split(/(^(?:.+\r?\n\r?(?:\=+|\-+)|#+.+|(?:~~~|```).*)\s*$)/).each do |part|
+          @text.split(/(^(?:\S+\r?\n\r?(?:\=+|\-+)|#+.+|(?:~~~|```).*)\s*$)/).each do |part|
             level = nil
             if part =~ /\A(~{3,}|`{3,})(\s*\S+)?\s*$/
               if !inside_pre
diff --git a/test/unit/lib/redmine/wiki_formatting/markdown_formatter_test.rb b/test/unit/lib/redmine/wiki_formatting/markdown_formatter_test.rb
index 561e7aa02..e3bb6ee79 100644
--- a/test/unit/lib/redmine/wiki_formatting/markdown_formatter_test.rb
+++ b/test/unit/lib/redmine/wiki_formatting/markdown_formatter_test.rb
@@ -180,6 +180,75 @@ class Redmine::WikiFormatting::MarkdownFormatterTest < ActionView::TestCase
     )
   end
 
+  STR_SETEXT_LIKE = [
+    # 0
+    <<~STR.chomp,
+      # Title
+    STR
+    # 1
+    <<~STR.chomp,
+      ## Heading 2
+
+      Thematic breaks - not be confused with setext headings.
+
+      ---
+
+      Preceding CRLF is the default for web-submitted data.
+      \r
+      ---\r
+      \r
+
+      A space-only line does not mean much.
+      \s
+      ---
+
+      End of thematic breaks.
+    STR
+    # 2
+    <<~STR.chomp,
+      ## Heading 2
+      Nulla nunc nisi, egestas in ornare vel, posuere ac libero.
+    STR
+  ]
+
+  STR_RARE_SETEXT_LIKE = [
+    # 0
+    <<~STR.chomp,
+      # Title
+    STR
+    # 1
+    <<~STR.chomp,
+      ## Heading 2
+
+      - item
+      one
+      -
+      not a heading
+    STR
+    # 2
+    <<~STR.chomp,
+      ## Heading 2
+      Nulla nunc nisi, egestas in ornare vel, posuere ac libero.
+    STR
+  ]
+
+  def test_get_section_should_ignore_setext_like_text
+    text = STR_SETEXT_LIKE.join("\n\n")
+    assert_section_with_hash STR_SETEXT_LIKE[1], text, 2
+    assert_section_with_hash STR_SETEXT_LIKE[2], text, 3
+  end
+
+  def test_get_section_should_ignore_rare_setext_like_text
+    begin
+      text = STR_RARE_SETEXT_LIKE.join("\n\n")
+      assert_section_with_hash STR_RARE_SETEXT_LIKE[1], text, 2
+      assert_section_with_hash STR_RARE_SETEXT_LIKE[2], text, 3
+    rescue Minitest::Assertion => e
+      skip "Section extraction is currently limited, see #35037. Known error: #{e.message}"
+    end
+    refute "This test should be adjusted when fixing the known error."
+  end
+
   def test_should_support_underlined_text
     text = 'This _text_ should be underlined'
     assert_equal '<p>This <u>text</u> should be underlined</p>', @formatter.new(text).to_html.strip