diff --git a/clang/lib/Format/FormatToken.h b/clang/lib/Format/FormatToken.h
--- a/clang/lib/Format/FormatToken.h
+++ b/clang/lib/Format/FormatToken.h
@@ -112,6 +112,7 @@
   TYPE(UntouchableMacroFunc)                                                   \
   TYPE(CSharpStringLiteral)                                                    \
   TYPE(CSharpNamedArgumentColon)                                               \
+  TYPE(CSharpNullable)                                                         \
   TYPE(CSharpNullConditionalLSquare)                                           \
   TYPE(CSharpGenericTypeConstraint)                                            \
   TYPE(CSharpGenericTypeConstraintColon)                                       \
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
@@ -1078,7 +1078,7 @@
             (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))) {
-          Tok->setType(TT_JsTypeOptionalQuestion);
+          Tok->setType(TT_CSharpNullable);
           break;
         }
       }
@@ -3161,7 +3161,7 @@
       return Style.SpacesInSquareBrackets;
 
     // No space before ? in nullable types.
-    if (Right.is(TT_JsTypeOptionalQuestion))
+    if (Right.is(TT_CSharpNullable))
       return false;
 
     // No space before null forgiving '!'.
@@ -3818,6 +3818,10 @@
     // Only break after commas for generic type constraints.
     if (Line.First->is(TT_CSharpGenericTypeConstraint))
       return Left.is(TT_CSharpGenericTypeConstraintComma);
+    // Keep nullable operators attached to their identifiers.
+    if (Right.is(TT_CSharpNullable)) {
+      return false;
+    }
   } else if (Style.Language == FormatStyle::LK_Java) {
     if (Left.isOneOf(Keywords.kw_throws, Keywords.kw_extends,
                      Keywords.kw_implements))
diff --git a/clang/lib/Format/UnwrappedLineParser.h b/clang/lib/Format/UnwrappedLineParser.h
--- a/clang/lib/Format/UnwrappedLineParser.h
+++ b/clang/lib/Format/UnwrappedLineParser.h
@@ -114,6 +114,7 @@
   void parseNew();
   void parseAccessSpecifier();
   bool parseEnum();
+  bool parseStructLike();
   void parseConcept();
   void parseRequires();
   void parseRequiresExpression(unsigned int OriginalLevel);
diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1316,15 +1316,7 @@
     case tok::kw_struct:
     case tok::kw_union:
     case tok::kw_class:
-      // parseRecord falls through and does not yet add an unwrapped line as a
-      // record declaration or definition can start a structural element.
-      parseRecord();
-      // This does not apply for Java, JavaScript and C#.
-      if (Style.Language == FormatStyle::LK_Java ||
-          Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp()) {
-        if (FormatTok->is(tok::semi))
-          nextToken();
-        addUnwrappedLine();
+      if (parseStructLike()) {
         return;
       }
       break;
@@ -1438,6 +1430,13 @@
         return;
       }
 
+      if (FormatTok->is(Keywords.kw_interface)) {
+        if (parseStructLike()) {
+          return;
+        }
+        break;
+      }
+
       if (Style.isCpp() && FormatTok->is(TT_StatementMacro)) {
         parseStatementMacro();
         return;
@@ -2525,6 +2524,21 @@
   // "} n, m;" will end up in one unwrapped line.
 }
 
+bool UnwrappedLineParser::parseStructLike() {
+  // parseRecord falls through and does not yet add an unwrapped line as a
+  // record declaration or definition can start a structural element.
+  parseRecord();
+  // This does not apply to Java, JavaScript and C#.
+  if (Style.Language == FormatStyle::LK_Java ||
+      Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp()) {
+    if (FormatTok->is(tok::semi))
+      nextToken();
+    addUnwrappedLine();
+    return true;
+  }
+  return false;
+}
+
 namespace {
 // A class used to set and restore the Token position when peeking
 // ahead in the token source.
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
@@ -848,6 +848,21 @@
   verifyFormat(R"(var x = (int?)y;)", Style); // Cast to a nullable type.
 
   verifyFormat(R"(var x = new MyContainer<int?>();)", Style); // Generics.
+
+  verifyFormat(R"(//
+public interface I {
+  int? Function();
+})",
+               Style); // Interface methods.
+
+  Style.ColumnLimit = 10;
+  verifyFormat(R"(//
+public VeryLongType? Function(
+    int arg1,
+    int arg2) {
+  //
+})",
+               Style); // ? sticks with identifier.
 }
 
 TEST_F(FormatTestCSharp, CSharpArraySubscripts) {