diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index f89b14995..512dc01ed 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -949,6 +949,7 @@ module ApplicationHelper
         send method_name, txt, project, obj, attr, only_path, options
       end
     end
+    unwrap_paragraphs_containing_block_macros(text)
     parse_headings(text, project, obj, attr, only_path, options)
 
     if @parsed_headings.any?
@@ -1468,6 +1469,20 @@ module ApplicationHelper
     end
   end
 
+  # Fixes invalid HTML where block-level elements from macros (e.g. collapse)
+  # are nested inside <p> tags. Replaces the <p></p> with <div></div> so that
+  # consecutive paragraphs remain visually separated as block-level elements.
+  # Uses a pattern that treats <div class="collapsed-text">...</div> as atomic
+  # so that </p> inside the div's content does not end the outer match early.
+  def unwrap_paragraphs_containing_block_macros(text)
+    collapsed_div = /<div[^>]*class="[^"]*collapsed-text[^"]*"[^>]*>(?:(?!<\/div>).)*<\/div>/m
+    non_collapsed = /(?!<\/p>)(?!<div[^>]*class="[^"]*collapsed-text)./m
+    text.gsub!(
+      /<p>(#{non_collapsed}*(?:#{collapsed_div}#{non_collapsed}*)+)<\/p>/m,
+      '<div>\1</div>'
+    )
+  end
+
   TOC_RE = /<p>\{\{((<|&lt;)|(>|&gt;))?toc\}\}<\/p>/i unless const_defined?(:TOC_RE)
 
   # Renders the TOC with given headings
diff --git a/test/unit/lib/redmine/wiki_formatting/macros_test.rb b/test/unit/lib/redmine/wiki_formatting/macros_test.rb
index 8c3011575..dc14ed8c0 100644
--- a/test/unit/lib/redmine/wiki_formatting/macros_test.rb
+++ b/test/unit/lib/redmine/wiki_formatting/macros_test.rb
@@ -314,6 +314,72 @@ class Redmine::WikiFormatting::MacrosTest < Redmine::HelperTest
     end
   end
 
+  COLLAPSE_INVALID_HTML_RE = /<p>(?:(?!<\/p>).)*<div[^>]*class="[^"]*collapsed-text/m
+
+  # Example 1: text between collapses in the same paragraph
+  def test_macro_multiple_collapse_with_text_between_should_not_generate_div_inside_p
+    text = <<~RAW
+      1 {{collapse(1)
+      content 1
+      }}
+      2 {{collapse(2)
+      content 2
+      }}
+      3 {{collapse(3)
+      content 3
+      }}
+    RAW
+    with_locale 'en' do
+      with_settings :text_formatting => 'textile' do
+        assert_no_match(COLLAPSE_INVALID_HTML_RE, textilizable(text))
+      end
+    end
+  end
+
+  # Example 2: adjacent collapses with no text between
+  def test_macro_multiple_collapse_adjacent_should_not_generate_div_inside_p
+    text = <<~RAW
+      {{collapse(1)
+      content 1
+      }}
+      {{collapse(2)
+      content 2
+      }}
+      {{collapse(3)
+      content 3
+      }}
+    RAW
+    with_locale 'en' do
+      with_settings :text_formatting => 'textile' do
+        assert_no_match(COLLAPSE_INVALID_HTML_RE, textilizable(text))
+      end
+    end
+  end
+
+  # Example 3: multiple groups of collapses separated by a blank line
+  def test_macro_multiple_collapse_groups_should_not_generate_div_inside_p
+    text = <<~RAW
+      1 {{collapse(1)
+      content 1
+      }}
+      2 {{collapse(2)
+      content 2
+      }}
+
+      3 {{collapse(3)
+      content 3
+      }}
+      4 {{collapse(4)
+      content 4
+      }}
+    RAW
+    with_locale 'en' do
+      with_settings :text_formatting => 'textile' do
+        assert_no_match(COLLAPSE_INVALID_HTML_RE, textilizable(text))
+      end
+    end
+  end
+
   def test_macro_child_pages
     expected =
       "<p><ul class=\"pages-hierarchy\">\n" \