Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -1312,11 +1312,34 @@
       if (Style.isCSharp()) {
         // `Type?)`, `Type?>`, `Type? name;` and `Type? name =` can only be
         // nullable types.
+
+        // `Type?)`, `Type?>`, `Type? name;`
+        if (Tok->Next &&
+            (Tok->Next->startsSequence(tok::question, tok::r_paren) ||
+             Tok->Next->startsSequence(tok::question, tok::greater) ||
+             Tok->Next->startsSequence(tok::question, tok::identifier,
+                                       tok::semi))) {
+          Tok->setType(TT_CSharpNullable);
+          break;
+        }
+
+        // `Type? name =`
+        if (Tok->Next && Tok->Next->is(tok::identifier) && Tok->Next->Next &&
+            Tok->Next->Next->is(tok::equal)) {
+          Tok->setType(TT_CSharpNullable);
+          break;
+        }
+
         // Line.MustBeDeclaration will be true for `Type? name;`.
-        if ((!Contexts.back().IsExpression && Line.MustBeDeclaration) ||
-            (Tok->Next && Tok->Next->isOneOf(tok::r_paren, tok::greater)) ||
-            (Tok->Next && Tok->Next->is(tok::identifier) && Tok->Next->Next &&
-             Tok->Next->Next->is(tok::equal))) {
+        // But not
+        // cond ? "A" : "B";
+        // cond ? id : "B";
+        // cond ? cond2 ? "A" : "B" : "C";
+        if (!Contexts.back().IsExpression && Line.MustBeDeclaration &&
+            (!Tok->Next ||
+             !Tok->Next->isOneOf(tok::identifier, tok::string_literal) ||
+             !Tok->Next->Next ||
+             !Tok->Next->Next->isOneOf(tok::colon, tok::question))) {
           Tok->setType(TT_CSharpNullable);
           break;
         }
Index: clang/unittests/Format/TokenAnnotatorTest.cpp
===================================================================
--- clang/unittests/Format/TokenAnnotatorTest.cpp
+++ clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -1724,6 +1724,34 @@
   EXPECT_TOKEN(Tokens[8], tok::l_paren, TT_ConditionLParen);
 }
 
+TEST_F(TokenAnnotatorTest, CSharpNullableTypes) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
+
+  auto Tokens = annotate("int? a;\n", Style);
+  EXPECT_EQ(Tokens.size(), 5u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::question, TT_CSharpNullable);
+
+  Tokens = annotate("int? a = 1;\n", Style);
+  EXPECT_EQ(Tokens.size(), 7u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::question, TT_CSharpNullable);
+
+  Tokens = annotate("int?)\n", Style);
+  EXPECT_EQ(Tokens.size(), 4u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::question, TT_CSharpNullable);
+
+  Tokens = annotate("int?>\n", Style);
+  EXPECT_EQ(Tokens.size(), 4u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::question, TT_CSharpNullable);
+
+  Tokens = annotate("cond? id : id2\n", Style);
+  EXPECT_EQ(Tokens.size(), 6u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::question, TT_ConditionalExpr);
+
+  Tokens = annotate("cond ? cond2 ? : id1 : id2\n", Style);
+  EXPECT_EQ(Tokens.size(), 9u) << Tokens;
+  EXPECT_TOKEN(Tokens[1], tok::question, TT_ConditionalExpr);
+}
+
 } // namespace
 } // namespace format
 } // namespace clang