diff --git a/HISTORY.md b/HISTORY.md
index 4e0dc5c..a1bf12f 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -2,8 +2,10 @@
 
 ## 4.0.1 (unreleased)
 
-
-- Nothing changed yet.
+- keep line breaks: Do not reformat class attribute values.
+  This allows for multi-line or otherwise manually strangely formatted
+  class attributes.
+  [thet]
 
 
 ## 4.0.0 (2026-04-10)
diff --git a/zpretty/attributes.py b/zpretty/attributes.py
index 05ec795..7ab080a 100644
--- a/zpretty/attributes.py
+++ b/zpretty/attributes.py
@@ -115,7 +115,8 @@ def sort_attributes(self, name):
         """
         if name.startswith("xmlns"):
             return (0, name)
-        if name in ("class", "id"):
+        # data-zpretty-class being the class replacement to avoid reformatting.
+        if name in ("class", "data-zpretty-class", "id"):
             return (100, name)
         if name.startswith("data"):
             return (300, name)
diff --git a/zpretty/prettifier.py b/zpretty/prettifier.py
index 097d89d..03dfbe2 100644
--- a/zpretty/prettifier.py
+++ b/zpretty/prettifier.py
@@ -23,6 +23,9 @@ class ZPrettifier:
     _ampersand_marker = str(uuid4())
     _cdata_marker = str(uuid4())
     _cdata_pattern = re.compile(r"<!\[CDATA\[(.*?)\]\]>", re.DOTALL)
+    _class_marker_name = "data-zpretty-class"
+    _class_marker = " data-zpretty-class="
+    _class_pattern = " class="
     _doctype_marker = f"<!DOCTYPE foo-{str(uuid4())}>"
     _doctype_pattern = re.compile(
         r"(<!DOCTYPE[^>[]*(\[[^]]*\])?>)", re.IGNORECASE | re.DOTALL
@@ -50,6 +53,14 @@ def __init__(self, filename="", text="", encoding="utf8"):
         # in the attributes so that bogus ones can be escaped
         for el in soup.descendants:
             attrs = getattr(el, "attrs", {})
+
+            # Restore class attributes.
+            # Beautiful soup changes the formatting of class attributes into a
+            # single-line attribute.
+            if self._class_marker_name in attrs:
+                attrs["class"] = attrs.get(self._class_marker_name)
+                del attrs[self._class_marker_name]
+
             for key, value in attrs.items():
                 if self._ampersand_marker in value:
                     attrs[key] = value.replace(self._ampersand_marker, "&")
@@ -122,6 +133,11 @@ def _prepare_text(self):
         text = re.sub(self._cdata_pattern, self._cdata_marker, text)
         text = re.sub(self._doctype_pattern, self._doctype_marker, text)
 
+        # Replace class attributes.
+        # Beautiful soup changes the formatting of class attributes into a
+        # single-line attribute, which we want to prevent.
+        text = re.sub(self._class_pattern, self._class_marker, text)
+
         # Get all the entities in the text and replace them with a marker
         # The text might contain undefined entities that BeautifulSoup
         # will strip out.
diff --git a/zpretty/tests/original/sample_pt.pt b/zpretty/tests/original/sample_pt.pt
index c563553..b657e10 100644
--- a/zpretty/tests/original/sample_pt.pt
+++ b/zpretty/tests/original/sample_pt.pt
@@ -39,6 +39,30 @@
           Foo
             Bar
         </pre>
+        <section class="class-a">
+          <div class="
+                 class-b
+                 class-c
+
+                 ${'class-d' if True else ''}
+                 button button-important
+                 pil pil-${'blue' if True else ''}
+
+                 pat-inject
+               "
+               data-pat-inject="
+                  source: .main-content .important-stuff;
+                  target: .class-b .target
+                  &amp;&amp;
+                  source: .header #logo;
+                  target: .logo;
+                  ${'add: class-d' if True else ''}
+                  history:;
+               "
+          >
+           okay
+          </div>
+        </section>
         <form action="#"
               method="post"
         >