diff --git a/CHANGES b/CHANGES
index f9f267c3a..0e03a3f0a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -77,6 +77,8 @@ Bugs fixed
   with size explicitly set in pixels) (fixed for ``'pdflatex'/'lualatex'`` only)
 * #8911: C++: remove the longest matching prefix in
   :confval:`cpp_index_common_prefix` instead of the first that matches.
+* C, properly reject function declarations when a keyword is used
+  as parameter name.
 
 Testing
 --------
diff --git a/sphinx/domains/c.py b/sphinx/domains/c.py
index 061010d66..79d4e145c 100644
--- a/sphinx/domains/c.py
+++ b/sphinx/domains/c.py
@@ -387,19 +387,6 @@ class ASTPostfixDec(ASTPostfixOp):
         signode.append(nodes.Text('--'))
 
 
-class ASTPostfixMember(ASTPostfixOp):
-    def __init__(self, name):
-        self.name = name
-
-    def _stringify(self, transform: StringifyTransform) -> str:
-        return '.' + transform(self.name)
-
-    def describe_signature(self, signode: TextElement, mode: str,
-                           env: "BuildEnvironment", symbol: "Symbol") -> None:
-        signode.append(nodes.Text('.'))
-        self.name.describe_signature(signode, 'noneIsName', env, symbol)
-
-
 class ASTPostfixMemberOfPointer(ASTPostfixOp):
     def __init__(self, name):
         self.name = name
@@ -2256,7 +2243,7 @@ class DefinitionParser(BaseParser):
         #  | postfix "[" expression "]"
         #  | postfix "[" braced-init-list [opt] "]"
         #  | postfix "(" expression-list [opt] ")"
-        #  | postfix "." id-expression
+        #  | postfix "." id-expression  // taken care of in primary by nested name
         #  | postfix "->" id-expression
         #  | postfix "++"
         #  | postfix "--"
@@ -2274,17 +2261,6 @@ class DefinitionParser(BaseParser):
                     self.fail("Expected ']' in end of postfix expression.")
                 postFixes.append(ASTPostfixArray(expr))
                 continue
-            if self.skip_string('.'):
-                if self.skip_string('*'):
-                    # don't steal the dot
-                    self.pos -= 2
-                elif self.skip_string('..'):
-                    # don't steal the dot
-                    self.pos -= 3
-                else:
-                    name = self._parse_nested_name()
-                    postFixes.append(ASTPostfixMember(name))
-                    continue
             if self.skip_string('->'):
                 if self.skip_string('*'):
                     # don't steal the arrow
@@ -2693,16 +2669,13 @@ class DefinitionParser(BaseParser):
     def _parse_declarator_name_suffix(
             self, named: Union[bool, str], paramMode: str, typed: bool
     ) -> ASTDeclarator:
+        assert named in (True, False, 'single')
         # now we should parse the name, and then suffixes
-        if named == 'maybe':
-            pos = self.pos
-            try:
-                declId = self._parse_nested_name()
-            except DefinitionError:
-                self.pos = pos
-                declId = None
-        elif named == 'single':
+        if named == 'single':
             if self.match(identifier_re):
+                if self.matched_text in _keywords:
+                    self.fail("Expected identifier, "
+                              "got keyword: %s" % self.matched_text)
                 identifier = ASTIdentifier(self.matched_text)
                 declId = ASTNestedName([identifier], rooted=False)
             else:
@@ -2880,8 +2853,8 @@ class DefinitionParser(BaseParser):
 
     def _parse_type(self, named: Union[bool, str], outer: str = None) -> ASTType:
         """
-        named=False|'maybe'|True: 'maybe' is e.g., for function objects which
-        doesn't need to name the arguments
+        named=False|'single'|True: 'single' is e.g., for function objects which
+        doesn't need to name the arguments, but otherwise is a single name
         """
         if outer:  # always named
             if outer not in ('type', 'member', 'function'):
diff --git a/tests/roots/test-domain-c/anon-dup-decl.rst b/tests/roots/test-domain-c/anon-dup-decl.rst
index 5f6c3bdfe..743ae2f6a 100644
--- a/tests/roots/test-domain-c/anon-dup-decl.rst
+++ b/tests/roots/test-domain-c/anon-dup-decl.rst
@@ -1,3 +1,5 @@
+.. c:namespace:: anon_dup_decl_ns
+
 .. c:struct:: anon_dup_decl
 
 	.. c:struct:: @a.A
diff --git a/tests/roots/test-domain-c/function_param_target.rst b/tests/roots/test-domain-c/function_param_target.rst
index 05de01445..d316d7bcd 100644
--- a/tests/roots/test-domain-c/function_param_target.rst
+++ b/tests/roots/test-domain-c/function_param_target.rst
@@ -1,3 +1,5 @@
+.. c:namespace:: function_param_target
+
 .. c:function:: void f(int i)
 
 	- :c:var:`i`
diff --git a/tests/roots/test-domain-c/index.rst b/tests/roots/test-domain-c/index.rst
index 7e2c18be9..4febd63ef 100644
--- a/tests/roots/test-domain-c/index.rst
+++ b/tests/roots/test-domain-c/index.rst
@@ -1,3 +1,5 @@
+.. c:namespace:: index
+
 test-domain-c
 =============
 
diff --git a/tests/roots/test-domain-c/semicolon.rst b/tests/roots/test-domain-c/semicolon.rst
deleted file mode 100644
index 14ba17756..000000000
--- a/tests/roots/test-domain-c/semicolon.rst
+++ /dev/null
@@ -1,10 +0,0 @@
-.. c:member:: int member;
-.. c:var:: int var;
-.. c:function:: void f();
-.. .. c:macro:: NO_SEMICOLON;
-.. c:struct:: Struct;
-.. c:union:: Union;
-.. c:enum:: Enum;
-.. c:enumerator:: Enumerator;
-.. c:type:: Type;
-.. c:type:: int TypeDef;
diff --git a/tests/test_domain_c.py b/tests/test_domain_c.py
index 2cfcf74fa..38e83a77e 100644
--- a/tests/test_domain_c.py
+++ b/tests/test_domain_c.py
@@ -417,6 +417,9 @@ def test_function_definitions():
     check('function', 'void f(int arr[const static volatile 42])', {1: 'f'},
           output='void f(int arr[static volatile const 42])')
 
+    with pytest.raises(DefinitionError):
+        parse('function', 'void f(int for)')
+
 
 def test_nested_name():
     check('struct', '{key}.A', {1: "A"})
@@ -523,8 +526,15 @@ def test_attributes():
 #     raise DefinitionError("")
 
 
+def split_warnigns(warning):
+    ws = warning.getvalue().split("\n")
+    assert len(ws) >= 1
+    assert ws[-1] == ""
+    return ws[:-1]
+
+
 def filter_warnings(warning, file):
-    lines = warning.getvalue().split("\n")
+    lines = split_warnigns(warning)
     res = [l for l in lines if "domain-c" in l and "{}.rst".format(file) in l and
            "WARNING: document isn't included in any toctree" not in l]
     print("Filtered warnings for file '{}':".format(file))
@@ -578,10 +588,22 @@ def test_build_domain_c_anon_dup_decl(app, status, warning):
     assert "WARNING: c:identifier reference target not found: @b" in ws[1]
 
 
-@pytest.mark.sphinx(testroot='domain-c', confoverrides={'nitpicky': True})
-def test_build_domain_c_semicolon(app, status, warning):
-    app.builder.build_all()
-    ws = filter_warnings(warning, "semicolon")
+@pytest.mark.sphinx(confoverrides={'nitpicky': True})
+def test_build_domain_c_semicolon(app, warning):
+    text = """
+.. c:member:: int member;
+.. c:var:: int var;
+.. c:function:: void f();
+.. .. c:macro:: NO_SEMICOLON;
+.. c:struct:: Struct;
+.. c:union:: Union;
+.. c:enum:: Enum;
+.. c:enumerator:: Enumerator;
+.. c:type:: Type;
+.. c:type:: int TypeDef;
+"""
+    restructuredtext.parse(app, text)
+    ws = split_warnigns(warning)
     assert len(ws) == 0
 
 
@@ -593,8 +615,8 @@ def test_build_function_param_target(app, warning):
     assert len(ws) == 0
     entries = extract_role_links(app, "function_param_target.html")
     assert entries == [
-        ('c.f', 'i', 'i'),
-        ('c.f', 'f.i', 'f.i'),
+        ('c.function_param_target.f', 'i', 'i'),
+        ('c.function_param_target.f', 'f.i', 'f.i'),
     ]
 
 
@@ -656,6 +678,8 @@ def test_noindexentry(app):
 
 @pytest.mark.sphinx(testroot='domain-c-intersphinx', confoverrides={'nitpicky': True})
 def test_intersphinx(tempdir, app, status, warning):
+    # a splitting of test_ids_vs_tags0 into the primary directives in a remote project,
+    # and then the references in the test project
     origSource = """\
 .. c:member:: int _member
 .. c:var:: int _var