diff --git a/CHANGES b/CHANGES
index 27268df662..7496960602 100644
--- a/CHANGES
+++ b/CHANGES
@@ -80,6 +80,9 @@ Features added
 Bugs fixed
 ----------
 
+* C, don't deepcopy the entire symbol table and make a mess every time an
+  enumerator is handled.
+
 Testing
 --------
 
diff --git a/sphinx/domains/c.py b/sphinx/domains/c.py
index 0e7d88e042..6c117a558c 100644
--- a/sphinx/domains/c.py
+++ b/sphinx/domains/c.py
@@ -1336,6 +1336,10 @@ class ASTDeclaration(ASTBaseBase):
         # set by CObject._add_enumerator_to_parent
         self.enumeratorScopedSymbol = None  # type: Symbol
 
+    def clone(self) -> "ASTDeclaration":
+        return ASTDeclaration(self.objectType, self.directiveType,
+                              self.declaration.clone(), self.semicolon)
+
     @property
     def name(self) -> ASTNestedName:
         return self.declaration.name
@@ -1425,6 +1429,16 @@ class Symbol:
     debug_lookup = False
     debug_show_tree = False
 
+    def __copy__(self):
+        assert False  # shouldn't happen
+
+    def __deepcopy__(self, memo):
+        if self.parent:
+            assert False  # shouldn't happen
+        else:
+            # the domain base class makes a copy of the initial data, which is fine
+            return Symbol(None, None, None, None)
+
     @staticmethod
     def debug_print(*args: Any) -> None:
         print(Symbol.debug_indent_string * Symbol.debug_indent, end="")
diff --git a/sphinx/domains/cpp.py b/sphinx/domains/cpp.py
index c840423aad..38c84898be 100644
--- a/sphinx/domains/cpp.py
+++ b/sphinx/domains/cpp.py
@@ -3782,6 +3782,16 @@ class Symbol:
     debug_lookup = False  # overridden by the corresponding config value
     debug_show_tree = False  # overridden by the corresponding config value
 
+    def __copy__(self):
+        assert False  # shouldn't happen
+
+    def __deepcopy__(self, memo):
+        if self.parent:
+            assert False  # shouldn't happen
+        else:
+            # the domain base class makes a copy of the initial data, which is fine
+            return Symbol(None, None, None, None, None, None)
+
     @staticmethod
     def debug_print(*args: Any) -> None:
         print(Symbol.debug_indent_string * Symbol.debug_indent, end="")
diff --git a/sphinx/util/cfamily.py b/sphinx/util/cfamily.py
index 6c2e99c842..a67b2a0add 100644
--- a/sphinx/util/cfamily.py
+++ b/sphinx/util/cfamily.py
@@ -110,7 +110,6 @@ class ASTBaseBase:
     __hash__ = None  # type: Callable[[], int]
 
     def clone(self) -> Any:
-        """Clone a definition expression node."""
         return deepcopy(self)
 
     def _stringify(self, transform: StringifyTransform) -> str: