diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -1011,7 +1011,12 @@
           Style.Language == FormatStyle::LK_JavaScript)
         break;
       if (Style.isCSharp()) {
-        if (Line.MustBeDeclaration && !Contexts.back().IsExpression) {
+        // `Type? name;` and `Type? name =` can only be nullable types.
+        // Line.MustBeDeclaration will be true for `Type? name;`.
+        if (!Contexts.back().IsExpression &&
+            (Line.MustBeDeclaration ||
+             (Tok->Next && Tok->Next->is(tok::identifier) && Tok->Next->Next &&
+              Tok->Next->Next->is(tok::equal)))) {
           Tok->Type = TT_CSharpNullable;
           break;
         }
diff --git a/clang/unittests/Format/FormatTestCSharp.cpp b/clang/unittests/Format/FormatTestCSharp.cpp
--- a/clang/unittests/Format/FormatTestCSharp.cpp
+++ b/clang/unittests/Format/FormatTestCSharp.cpp
@@ -631,7 +631,17 @@
   FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
   Style.SpacesInSquareBrackets = false;
 
+  verifyFormat(R"(//
+public class A {
+  void foo() { int? value = some.bar(); }
+})",
+               Style); // int? is nullable not a conditional expression.
+
+  verifyFormat(R"(void foo(int? x, int? y, int? z) {})",
+               Style); // Nullables in function definitions.
+
   verifyFormat(R"(public float? Value;)", Style); // no space before `?`.
+
   verifyFormat(R"(int?[] arr = new int?[10];)",
                Style); // An array of a nullable type.
 }