diff --git a/sphinx/ext/jsmath.py b/sphinx/ext/jsmath.py
index 3babd408e..e03351800 100644
--- a/sphinx/ext/jsmath.py
+++ b/sphinx/ext/jsmath.py
@@ -22,6 +22,7 @@ if False:
     from typing import Any, Dict  # NOQA
     from sphinx.application import Sphinx  # NOQA
     from sphinx.environment import BuildEnvironment  # NOQA
+    from sphinx.writers.html import HTMLTranslator  # NOQA
 
 
 def html_visit_math(self, node):
@@ -32,7 +33,7 @@ def html_visit_math(self, node):
 
 
 def html_visit_displaymath(self, node):
-    # type: (nodes.NodeVisitor, nodes.Node) -> None
+    # type: (HTMLTranslator, nodes.Node) -> None
     if node['nowrap']:
         self.body.append(self.starttag(node, 'div', CLASS='math notranslate nohighlight'))
         self.body.append(self.encode(node.astext()))
diff --git a/sphinx/ext/mathjax.py b/sphinx/ext/mathjax.py
index 21406c451..3786c8107 100644
--- a/sphinx/ext/mathjax.py
+++ b/sphinx/ext/mathjax.py
@@ -25,6 +25,7 @@ if False:
     from typing import Any, Dict  # NOQA
     from sphinx.application import Sphinx  # NOQA
     from sphinx.environment import BuildEnvironment  # NOQA
+    from sphinx.writers.html import HTMLTranslator  # NOQA
 
 
 def html_visit_math(self, node):
@@ -37,7 +38,7 @@ def html_visit_math(self, node):
 
 
 def html_visit_displaymath(self, node):
-    # type: (nodes.NodeVisitor, nodes.Node) -> None
+    # type: (HTMLTranslator, nodes.Node) -> None
     self.body.append(self.starttag(node, 'div', CLASS='math notranslate nohighlight'))
     if node['nowrap']:
         self.body.append(self.encode(node.astext()))
diff --git a/sphinx/util/math.py b/sphinx/util/math.py
index b960613c0..58f8a17d0 100644
--- a/sphinx/util/math.py
+++ b/sphinx/util/math.py
@@ -13,11 +13,11 @@
 if False:
     # For type annotation
     from docutils import nodes  # NOQA
-    from docutils.writers.html4css1 import Writer  # NOQA
+    from sphinx.builders.html import HTMLTranslator  # NOQA
 
 
 def get_node_equation_number(writer, node):
-    # type: (Writer, nodes.Node) -> unicode
+    # type: (HTMLTranslator, nodes.Node) -> unicode
     if writer.builder.config.math_numfig and writer.builder.config.numfig:
         figtype = 'displaymath'
         if writer.builder.name == 'singlehtml':
@@ -27,11 +27,9 @@ def get_node_equation_number(writer, node):
 
         id = node['ids'][0]
         number = writer.builder.fignumbers.get(key, {}).get(id, ())
-        number = '.'.join(map(str, number))
+        return '.'.join(map(str, number))
     else:
-        number = node['number']
-
-    return number
+        return node['number']
 
 
 def wrap_displaymath(text, label, numbering):