Index: clang/lib/Format/FormatToken.h
===================================================================
--- clang/lib/Format/FormatToken.h
+++ clang/lib/Format/FormatToken.h
@@ -104,6 +104,7 @@
   TYPE(CSharpStringLiteral)                                                    \
   TYPE(CSharpNullCoalescing)                                                   \
   TYPE(CSharpNamedArgumentColon)                                               \
+  TYPE(CSharpNullableTypeQuestionMark)                                         \
   TYPE(Unknown)
 
 enum TokenType {
Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -987,6 +987,10 @@
       if (Line.MustBeDeclaration && !Contexts.back().IsExpression &&
           Style.Language == FormatStyle::LK_JavaScript)
         break;
+      if (Style.isCSharp() && Line.MustBeDeclaration) {
+        Tok->Type = TT_CSharpNullableTypeQuestionMark;
+        break;
+      }
       parseConditional();
       break;
     case tok::kw_template:
@@ -2902,6 +2906,10 @@
     if (Left.is(tok::comma) && Right.is(tok::r_square))
       return Style.SpacesInSquareBrackets;
 
+    // No space before ? in nullable types.
+    if (Right.is(TT_CSharpNullableTypeQuestionMark))
+      return false;
+
     // space between keywords and paren e.g. "using ("
     if (Right.is(tok::l_paren))
       if (Left.isOneOf(tok::kw_using, Keywords.kw_async, Keywords.kw_when))
Index: clang/unittests/Format/FormatTestCSharp.cpp
===================================================================
--- clang/unittests/Format/FormatTestCSharp.cpp
+++ clang/unittests/Format/FormatTestCSharp.cpp
@@ -175,7 +175,7 @@
   Style.SpaceBeforeParens = FormatStyle::SBPO_Always;
 
   verifyFormat(
-      "public Person(string firstName, string lastName, int? age=null)");
+      "public Person(string firstName, string lastName, int? age = null)");
 
   verifyFormat("foo () {\n"
                "  switch (args?.Length) {}\n"
@@ -603,5 +603,11 @@
   verifyFormat(R"(private float[, ] Values;)", Style);
 }
 
+TEST_F(FormatTestCSharp, CSharpNullableTypes) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
+
+  verifyFormat(R"(public float? Value;)", Style); // no space before `?`.
+}
+
 } // namespace format
 } // end namespace clang