diff --git a/clang/lib/Tooling/Syntax/BuildTree.cpp b/clang/lib/Tooling/Syntax/BuildTree.cpp
--- a/clang/lib/Tooling/Syntax/BuildTree.cpp
+++ b/clang/lib/Tooling/Syntax/BuildTree.cpp
@@ -624,6 +624,9 @@
   }
 
   bool WalkUpFromDeclRefExpr(DeclRefExpr *S) {
+    if (S->getNameInfo().getName().getNameKind() ==
+        clang::DeclarationName::CXXLiteralOperatorName)
+      return true;
     if (auto *NNS = BuildNestedNameSpecifier(S->getQualifierLoc()))
       Builder.markChild(NNS, syntax::NodeRole::IdExpression_qualifier);
 
diff --git a/clang/unittests/Tooling/Syntax/TreeTest.cpp b/clang/unittests/Tooling/Syntax/TreeTest.cpp
--- a/clang/unittests/Tooling/Syntax/TreeTest.cpp
+++ b/clang/unittests/Tooling/Syntax/TreeTest.cpp
@@ -1228,6 +1228,95 @@
 )txt"));
 }
 
+TEST_P(SyntaxTreeTest, UserDefinedLiteral) {
+  if (!GetParam().isCXX11OrLater()) {
+    return;
+  }
+  EXPECT_TRUE(treeDumpEqual(
+      R"cpp(
+long double operator "" _w(long double);
+unsigned operator "" _w(const char*);
+template <char...> unsigned operator "" _x();
+int main() {
+    1.2_w; // calls operator "" _w(1.2L)
+    12_w;  // calls operator "" _w("12")
+    12_x;  // calls operator<'1', '2'> "" _x()
+}
+    )cpp",
+      R"txt(
+*: TranslationUnit
+|-SimpleDeclaration
+| |-long
+| |-double
+| |-SimpleDeclarator
+| | |-operator
+| | |-""
+| | |-_w
+| | `-ParametersAndQualifiers
+| |   |-(
+| |   |-SimpleDeclaration
+| |   | |-long
+| |   | `-double
+| |   `-)
+| `-;
+|-SimpleDeclaration
+| |-unsigned
+| |-SimpleDeclarator
+| | |-operator
+| | |-""
+| | |-_w
+| | `-ParametersAndQualifiers
+| |   |-(
+| |   |-SimpleDeclaration
+| |   | |-const
+| |   | |-char
+| |   | `-SimpleDeclarator
+| |   |   `-*
+| |   `-)
+| `-;
+|-TemplateDeclaration
+| |-template
+| |-<
+| |-SimpleDeclaration
+| | `-char
+| |-...
+| |->
+| `-SimpleDeclaration
+|   |-unsigned
+|   |-SimpleDeclarator
+|   | |-operator
+|   | |-""
+|   | |-_x
+|   | `-ParametersAndQualifiers
+|   |   |-(
+|   |   `-)
+|   `-;
+`-SimpleDeclaration
+  |-int
+  |-SimpleDeclarator
+  | |-main
+  | `-ParametersAndQualifiers
+  |   |-(
+  |   `-)
+  `-CompoundStatement
+    |-{
+    |-ExpressionStatement
+    | |-UnknownExpression
+    | | `-UnknownExpression
+    | |   `-1.2_w
+    | `-;
+    |-ExpressionStatement
+    | |-UnknownExpression
+    | | `-UnknownExpression
+    | |   `-12_w
+    | `-;
+    |-ExpressionStatement
+    | |-UnknownExpression
+    | | `-12_x
+    | `-;
+    `-}
+)txt"));
+}
 TEST_P(SyntaxTreeTest, IntegerLiteral) {
   EXPECT_TRUE(treeDumpEqual(
       R"cpp(