diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5923feb..37cbeb8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 - Remove the no longer needed escape_once helper call in node.haml, relying on HAML's global escape_html instead (@robertcheramy)
 - Update web libraries to the latest versions (@robertcheramy)
 - Encode JSON output with the standard library instead of Sinatra's json helper (@robertcheramy)
+- Set HAML's `attr_quote` explicitly to `"` for stable output across HAML versions (@robertcheramy)
 
 ### Fixed
 - Fix XSS vulnerability (CWE-79) by enabling HAML's escape_html globally; user-controlled values in node names, group names, model names, and URL parameters are now HTML-escaped in all templates (@mattimustang)
diff --git a/lib/oxidized/web/webapp.rb b/lib/oxidized/web/webapp.rb
index edaa77f..c3bc1e0 100644
--- a/lib/oxidized/web/webapp.rb
+++ b/lib/oxidized/web/webapp.rb
@@ -10,7 +10,10 @@ module API
     class WebApp < Sinatra::Base
       helpers Sinatra::UrlForHelper
       set :public_folder, proc { File.join(root, 'public') }
-      set :haml, { escape_html: true }
+      # attr_quote: use double quotes for HTML attributes. Set explicitly so the
+      # output is stable across Haml versions. Haml 7.3.0 changed the default
+      # from "'" to '"' (haml/haml#1188); older versions still default to "'".
+      set :haml, { escape_html: true, attr_quote: '"' }
 
       get '/' do
         redirect url_for('/nodes')
diff --git a/oxidized-web.gemspec b/oxidized-web.gemspec
index 20d2652..ce3e1f9 100644
--- a/oxidized-web.gemspec
+++ b/oxidized-web.gemspec
@@ -37,7 +37,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'emk-sinatra-url-for', '~> 0.2'
   # HAML 7.0.0 changed default attr_quote from ' to ".
   # Updating needs the unit tests to be fixed.
-  s.add_dependency 'haml',                '>= 6', '<7'
+  s.add_dependency 'haml',                '>= 6', '< 8'
   s.add_dependency 'htmlentities',        '~> 4.3'
   s.add_dependency 'json',                '~> 2.3'
   # Only depend on a minimal version of Oxidized so we don't need to
diff --git a/spec/web/node/version_spec.rb b/spec/web/node/version_spec.rb
index 87b1852..9dcc24b 100644
--- a/spec/web/node/version_spec.rb
+++ b/spec/web/node/version_spec.rb
@@ -27,26 +27,26 @@ def app
       get '/node/version?node_full=sw5'
       _(last_response.ok?).must_equal true
       _(last_response.body.include?(
-          "<tr>\n<td>3</td>\n<td class='time' epoch='1738781340'>" \
+          "<tr>\n<td>3</td>\n<td class=\"time\" epoch=\"1738781340\">" \
           "2025-02-05 19:49:00 +0100</td>\n"
         )).must_equal true
 
       _(last_response.body.include?(
-          "href='/node/version/view?node=sw5&amp;group=&amp;oid=C006&amp;" \
-          "epoch=1738781340&amp;num=3' title='configuration'>"
+          "href=\"/node/version/view?node=sw5&amp;group=&amp;oid=C006&amp;" \
+          "epoch=1738781340&amp;num=3\" title=\"configuration\">"
         )).must_equal true
       _(last_response.body.include?(
-          "href='/node/version/diffs?node=sw5&amp;group=&amp;oid=C006&amp;" \
-          "epoch=1738781340&amp;num=3' title='Compare with previous version'>"
+          "href=\"/node/version/diffs?node=sw5&amp;group=&amp;oid=C006&amp;" \
+          "epoch=1738781340&amp;num=3\" title=\"Compare with previous version\">"
         )).must_equal true
       _(last_response.body.include?(
-          "href='/node/version/view?node=sw5&amp;group=&amp;oid=C001&amp;" \
-          "epoch=1738778460&amp;num=1' title='configuration'>"
+          "href=\"/node/version/view?node=sw5&amp;group=&amp;oid=C001&amp;" \
+          "epoch=1738778460&amp;num=1\" title=\"configuration\">"
         )).must_equal true
       # Compare to the version previous 1 is not possible, so don't display it
       _(last_response.body.include?(
-          "href='/node/version/diffs?node=sw5&amp;group=&amp;oid=C001&amp;" \
-          "epoch=1738778460&amp;num=1' title='Compare with previous version'>"
+          "href=\"/node/version/diffs?node=sw5&amp;group=&amp;oid=C001&amp;" \
+          "epoch=1738778460&amp;num=1\" title=\"Compare with previous version\">"
         )).must_equal false
     end
 
@@ -56,7 +56,7 @@ def app
       get '/node/version?node_full=group1/sw5'
       _(last_response.ok?).must_equal true
       _(last_response.body.include?(
-          "<tr>\n<td>3</td>\n<td class='time' epoch='1738781340'>" \
+          "<tr>\n<td>3</td>\n<td class=\"time\" epoch=\"1738781340\">" \
           "2025-02-05 19:49:00 +0100</td>\n"
         )).must_equal true
     end
@@ -67,7 +67,7 @@ def app
       get '/node/version?node_full=gr/oup1/sw5'
       _(last_response.ok?).must_equal true
       _(last_response.body.include?(
-          "<tr>\n<td>3</td>\n<td class='time' epoch='1738781340'>" \
+          "<tr>\n<td>3</td>\n<td class=\"time\" epoch=\"1738781340\">" \
           "2025-02-05 19:49:00 +0100</td>\n"
         )).must_equal true
     end
@@ -84,7 +84,7 @@ def app
       # right string
       _(last_response.body.include?(
           "Date of version:\n" \
-          "<span class='time' epoch='1738781340'>" \
+          "<span class=\"time\" epoch=\"1738781340\">" \
           "#{Time.at(1738781340)}</span>"
         )).must_equal true
     end
@@ -153,7 +153,7 @@ def app
       # right string
       _(last_response.body.include?(
           "Date of version:\n" \
-          "<span class='time' epoch='1738781340'>" \
+          "<span class=\"time\" epoch=\"1738781340\">" \
           "#{Time.at(1738781340)}</span>"
         )).must_equal true
     end