diff --git a/html_sanitizer/sanitizer.py b/html_sanitizer/sanitizer.py
index 81a1d16..a8436f0 100644
--- a/html_sanitizer/sanitizer.py
+++ b/html_sanitizer/sanitizer.py
@@ -138,6 +138,14 @@ def __init__(self, settings=None):
                 set(self.attributes.keys()) - self.tags,
             ))
 
+    @staticmethod
+    def is_mergeable(e1, e2):
+        """
+        Decide if the adjacent elements of the same type e1 and e2 can be
+        merged. This can be overriden to honouring distinct classes etc.
+        """
+        return True
+
     def sanitize(self, html):
         """
         Clean HTML code from ugly copy-pasted CSS and empty elements
@@ -232,7 +240,8 @@ def sanitize(self, html):
                 # tag type
                 nx = element.getnext()
                 if (whitespace_re.match(element.tail or '') and
-                        nx is not None and nx.tag == element.tag):
+                        nx is not None and nx.tag == element.tag and
+                        self.is_mergeable(element, nx)):
                     # Yes, we should. Tail is empty, that is, no text between
                     # tags of a mergeable type.
                     if nx.text:
diff --git a/html_sanitizer/tests.py b/html_sanitizer/tests.py
index c409906..ab27c42 100644
--- a/html_sanitizer/tests.py
+++ b/html_sanitizer/tests.py
@@ -255,6 +255,9 @@ def test_14_classes(self):
         ), (
             '<p class="centered">Test <span class="bla">span</span></p>',
             '<p class="centered">Test <span class="bla">span</span></p>',
+        ), (
+            '<p class="centered">Test <span class="bla">span</span><span class="blub">span</span></p>',
+            '<p class="centered">Test <span class="bla">span span</span></p>',
         ), (
             '<h1 class="centered">Test</h1>',
             '<h1 class="centered">Test</h1>',
@@ -263,7 +266,30 @@ def test_14_classes(self):
             '<h2>Test</h2>',
         )], sanitizer=sanitizer)
 
-    def test_15_emoji(self):
+    def test_15_classes(self):
+        """Class attributes may disable merging"""
+        sanitizer = Sanitizer({
+            'tags': {'h1', 'h2', 'p', 'a', 'span'},
+            'attributes': {
+                'a': ('href', 'name', 'target', 'title', 'id'),
+                'h1': ('class',),
+                'p': ('class',),
+                'span': ('class',),
+            },
+            'empty': set(),
+            'separate': {'a', 'p'},
+            'is_mergeable': lambda e1, e2: e1.get('class') == e2.get('class'),
+        })
+
+        self.run_tests([(
+            '<p class="centered">Test <span class="bla">span</span><span class="blub">span</span></p>',
+            '<p class="centered">Test <span class="bla">span</span><span class="blub">span</span></p>',
+        ), (
+            '<p class="centered">Test <span class="bla">span</span><span class="bla">span</span></p>',
+            '<p class="centered">Test <span class="bla">span span</span></p>',
+        )], sanitizer=sanitizer)
+
+    def test_16_emoji(self):
         self.run_tests([(
             '<p>😂</p>',
             '<p>😂</p>',