diff --git a/flang/include/flang/Parser/dump-parse-tree.h b/flang/include/flang/Parser/dump-parse-tree.h
index 11725991e9c9a..49eeed0e7b439 100644
--- a/flang/include/flang/Parser/dump-parse-tree.h
+++ b/flang/include/flang/Parser/dump-parse-tree.h
@@ -479,7 +479,7 @@ class ParseTreeDumper {
   NODE(parser, OmpTraitPropertyName)
   NODE(parser, OmpTraitScore)
   NODE(parser, OmpTraitPropertyExtension)
-  NODE(OmpTraitPropertyExtension, ExtensionValue)
+  NODE(OmpTraitPropertyExtension, Complex)
   NODE(parser, OmpTraitProperty)
   NODE(parser, OmpTraitSelectorName)
   NODE_ENUM(OmpTraitSelectorName, Value)
diff --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
index 00d85aa05fb3a..88ce141d17cf9 100644
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -3505,37 +3505,22 @@ struct OmpTraitScore {
 };
 
 // trait-property-extension ->
-//    trait-property-name (trait-property-value, ...)
-// trait-property-value ->
 //    trait-property-name |
-//    scalar-integer-expression |
-//    trait-property-extension
-//
-// The grammar in OpenMP 5.2+ spec is ambiguous, the above is a different
-// version (but equivalent) that doesn't have ambiguities.
-// The ambiguity is in
-//   trait-property:
-//      trait-property-name          <- (a)
-//      trait-property-clause
-//      trait-property-expression    <- (b)
-//      trait-property-extension     <- this conflicts with (a) and (b)
-//   trait-property-extension:
-//      trait-property-name          <- conflict with (a)
-//      identifier(trait-property-extension[, trait-property-extension[, ...]])
-//      constant integer expression  <- conflict with (b)
+//    scalar-expr |
+//    trait-property-name (trait-property-extension, ...)
 //
 struct OmpTraitPropertyExtension {
   CharBlock source;
-  TUPLE_CLASS_BOILERPLATE(OmpTraitPropertyExtension);
-  struct ExtensionValue {
+  UNION_CLASS_BOILERPLATE(OmpTraitPropertyExtension);
+  struct Complex { // name (prop-ext, prop-ext, ...)
     CharBlock source;
-    UNION_CLASS_BOILERPLATE(ExtensionValue);
-    std::variant<OmpTraitPropertyName, ScalarExpr,
-        common::Indirection<OmpTraitPropertyExtension>>
-        u;
+    TUPLE_CLASS_BOILERPLATE(Complex);
+    std::tuple<OmpTraitPropertyName,
+        std::list<common::Indirection<OmpTraitPropertyExtension>>>
+        t;
   };
-  using ExtensionList = std::list<ExtensionValue>;
-  std::tuple<OmpTraitPropertyName, ExtensionList> t;
+
+  std::variant<OmpTraitPropertyName, ScalarExpr, Complex> u;
 };
 
 // trait-property ->
@@ -3568,9 +3553,10 @@ struct OmpTraitProperty {
 //    UID |               T        // unique-string-id /impl-defined
 //    VENDOR |            I        // name-list (vendor-id /add-def-doc)
 //    EXTENSION |         I        // name-list (ext_name /impl-defined)
-//    ATOMIC_DEFAULT_MEM_ORDER I | // value of admo
+//    ATOMIC_DEFAULT_MEM_ORDER I | // clause-list (value of admo)
 //    REQUIRES |          I        // clause-list (from requires)
 //    CONDITION           U        // logical-expr
+//    <other name>        I        // treated as extension
 //
 // Trait-set-selectors:
 //    [D]evice, [T]arget_device, [C]onstruct, [I]mplementation, [U]ser.
@@ -3579,7 +3565,7 @@ struct OmpTraitSelectorName {
   UNION_CLASS_BOILERPLATE(OmpTraitSelectorName);
   ENUM_CLASS(Value, Arch, Atomic_Default_Mem_Order, Condition, Device_Num,
       Extension, Isa, Kind, Requires, Simd, Uid, Vendor)
-  std::variant<Value, llvm::omp::Directive> u;
+  std::variant<Value, llvm::omp::Directive, std::string> u;
 };
 
 // trait-selector ->
diff --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
index 5ff91da082c85..30e4d4d491d58 100644
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -158,75 +158,153 @@ static TypeDeclarationStmt makeIterSpecDecl(std::list<ObjectName> &&names) {
 static std::string nameToString(Name &&name) { return name.ToString(); }
 
 TYPE_PARSER(sourced(construct<OmpTraitPropertyName>( //
-    (space >> charLiteralConstantWithoutKind) ||
-    applyFunction(nameToString, Parser<Name>{}))))
+    construct<OmpTraitPropertyName>(space >> charLiteralConstantWithoutKind) ||
+    construct<OmpTraitPropertyName>(
+        applyFunction(nameToString, Parser<Name>{})))))
 
 TYPE_PARSER(sourced(construct<OmpTraitScore>( //
-    "SCORE" >> parenthesized(scalarIntExpr))))
+    "SCORE"_id >> parenthesized(scalarIntExpr))))
 
-TYPE_PARSER(sourced(construct<OmpTraitPropertyExtension::ExtensionValue>(
-    // Parse nested extension first.
-    construct<OmpTraitPropertyExtension::ExtensionValue>(
-        indirect(Parser<OmpTraitPropertyExtension>{})) ||
-    construct<OmpTraitPropertyExtension::ExtensionValue>(
-        Parser<OmpTraitPropertyName>{}) ||
-    construct<OmpTraitPropertyExtension::ExtensionValue>(scalarExpr))))
-
-TYPE_PARSER(sourced(construct<OmpTraitPropertyExtension>( //
+TYPE_PARSER(sourced(construct<OmpTraitPropertyExtension::Complex>(
     Parser<OmpTraitPropertyName>{},
     parenthesized(nonemptySeparated(
-        Parser<OmpTraitPropertyExtension::ExtensionValue>{}, ","_tok)))))
+        indirect(Parser<OmpTraitPropertyExtension>{}), ",")))))
 
-TYPE_PARSER(sourced(construct<OmpTraitProperty>(
-    // Try clause first, then extension before OmpTraitPropertyName.
-    construct<OmpTraitProperty>(indirect(Parser<OmpClause>{})) ||
-    construct<OmpTraitProperty>(Parser<OmpTraitPropertyExtension>{}) ||
-    construct<OmpTraitProperty>(Parser<OmpTraitPropertyName>{}) ||
-    construct<OmpTraitProperty>(scalarExpr))))
+TYPE_PARSER(sourced(construct<OmpTraitPropertyExtension>(
+    construct<OmpTraitPropertyExtension>(
+        Parser<OmpTraitPropertyExtension::Complex>{}) ||
+    construct<OmpTraitPropertyExtension>(Parser<OmpTraitPropertyName>{}) ||
+    construct<OmpTraitPropertyExtension>(scalarExpr))))
 
 TYPE_PARSER(construct<OmpTraitSelectorName::Value>(
-    "ARCH" >> pure(OmpTraitSelectorName::Value::Arch) ||
-    "ATOMIC_DEFAULT_MEM_ORDER" >>
+    "ARCH"_id >> pure(OmpTraitSelectorName::Value::Arch) ||
+    "ATOMIC_DEFAULT_MEM_ORDER"_id >>
         pure(OmpTraitSelectorName::Value::Atomic_Default_Mem_Order) ||
-    "CONDITION" >> pure(OmpTraitSelectorName::Value::Condition) ||
-    "DEVICE_NUM" >> pure(OmpTraitSelectorName::Value::Device_Num) ||
-    "EXTENSION" >> pure(OmpTraitSelectorName::Value::Extension) ||
-    "ISA" >> pure(OmpTraitSelectorName::Value::Isa) ||
-    "KIND" >> pure(OmpTraitSelectorName::Value::Kind) ||
-    "REQUIRES" >> pure(OmpTraitSelectorName::Value::Requires) ||
-    "SIMD" >> pure(OmpTraitSelectorName::Value::Simd) ||
-    "UID" >> pure(OmpTraitSelectorName::Value::Uid) ||
-    "VENDOR" >> pure(OmpTraitSelectorName::Value::Vendor)))
+    "CONDITION"_id >> pure(OmpTraitSelectorName::Value::Condition) ||
+    "DEVICE_NUM"_id >> pure(OmpTraitSelectorName::Value::Device_Num) ||
+    "EXTENSION"_id >> pure(OmpTraitSelectorName::Value::Extension) ||
+    "ISA"_id >> pure(OmpTraitSelectorName::Value::Isa) ||
+    "KIND"_id >> pure(OmpTraitSelectorName::Value::Kind) ||
+    "REQUIRES"_id >> pure(OmpTraitSelectorName::Value::Requires) ||
+    "SIMD"_id >> pure(OmpTraitSelectorName::Value::Simd) ||
+    "UID"_id >> pure(OmpTraitSelectorName::Value::Uid) ||
+    "VENDOR"_id >> pure(OmpTraitSelectorName::Value::Vendor)))
 
 TYPE_PARSER(sourced(construct<OmpTraitSelectorName>(
     // Parse predefined names first (because of SIMD).
     construct<OmpTraitSelectorName>(Parser<OmpTraitSelectorName::Value>{}) ||
-    construct<OmpTraitSelectorName>(OmpDirectiveNameParser{}))))
+    construct<OmpTraitSelectorName>(OmpDirectiveNameParser{}) ||
+    // identifier-or-string for extensions
+    construct<OmpTraitSelectorName>(
+        applyFunction(nameToString, Parser<Name>{})) ||
+    construct<OmpTraitSelectorName>(space >> charLiteralConstantWithoutKind))))
+
+// Parser for OmpTraitSelector::Properties
+template <typename... PropParser>
+static constexpr auto propertyListParser(PropParser... pp) {
+  // Parse the property list "(score(expr): item1...)" in three steps:
+  // 1. Parse the "("
+  // 2. Parse the optional "score(expr):"
+  // 3. Parse the "item1, ...)", together with the ")".
+  // The reason for including the ")" in the 3rd step is to force parsing
+  // the entire list in each of the alternative property parsers. Otherwise,
+  // the name parser could stop after "foo" in "(foo, bar(1))", without
+  // allowing the next parser to give the list a try.
+  auto listOf{[](auto parser) { //
+    return nonemptySeparated(parser, ",");
+  }};
+
+  using P = OmpTraitProperty;
+  return maybe("(" >> //
+      construct<OmpTraitSelector::Properties>(
+          maybe(Parser<OmpTraitScore>{} / ":"),
+          (attempt(listOf(sourced(construct<P>(pp))) / ")") || ...)));
+}
+
+// Parser for OmpTraitSelector
+struct TraitSelectorParser {
+  using resultType = OmpTraitSelector;
+
+  constexpr TraitSelectorParser(Parser<OmpTraitSelectorName> p) : np(p) {}
 
-TYPE_PARSER(construct<OmpTraitSelector::Properties>(
-    maybe(Parser<OmpTraitScore>{} / ":"_tok),
-    nonemptySeparated(Parser<OmpTraitProperty>{}, ","_tok)))
+  std::optional<resultType> Parse(ParseState &state) const {
+    auto name{attempt(np).Parse(state)};
+    if (!name.has_value()) {
+      return std::nullopt;
+    }
+
+    // Default fallback parser for lists that cannot be parser using the
+    // primary property parser.
+    auto extParser{Parser<OmpTraitPropertyExtension>{}};
+
+    if (auto *v{std::get_if<OmpTraitSelectorName::Value>(&name->u)}) {
+      // (*) The comments below show the sections of the OpenMP spec that
+      // describe given trait. The cases marked with a (*) are those where
+      // the spec doesn't assign any list-type to these traits, but for
+      // convenience they can be treated as if they were.
+      switch (*v) {
+      // name-list properties
+      case OmpTraitSelectorName::Value::Arch: // [6.0:319:18]
+      case OmpTraitSelectorName::Value::Extension: // [6.0:319:30]
+      case OmpTraitSelectorName::Value::Isa: // [6.0:319:15]
+      case OmpTraitSelectorName::Value::Kind: // [6.0:319:10]
+      case OmpTraitSelectorName::Value::Uid: // [6.0:319:23](*)
+      case OmpTraitSelectorName::Value::Vendor: { // [6.0:319:27]
+        auto pp{propertyListParser(Parser<OmpTraitPropertyName>{}, extParser)};
+        return OmpTraitSelector(std::move(*name), std::move(*pp.Parse(state)));
+      }
+      // clause-list
+      case OmpTraitSelectorName::Value::Atomic_Default_Mem_Order:
+        // [6.0:321:26-29](*)
+      case OmpTraitSelectorName::Value::Requires: // [6.0:319:33]
+      case OmpTraitSelectorName::Value::Simd: { // [6.0:318:31]
+        auto pp{propertyListParser(indirect(Parser<OmpClause>{}), extParser)};
+        return OmpTraitSelector(std::move(*name), std::move(*pp.Parse(state)));
+      }
+      // expr-list
+      case OmpTraitSelectorName::Value::Condition: // [6.0:321:33](*)
+      case OmpTraitSelectorName::Value::Device_Num: { // [6.0:321:23-24](*)
+        auto pp{propertyListParser(scalarExpr, extParser)};
+        return OmpTraitSelector(std::move(*name), std::move(*pp.Parse(state)));
+      }
+      } // switch
+    } else {
+      // The other alternatives are `llvm::omp::Directive`, and `std::string`.
+      // The former doesn't take any properties[1], the latter is a name of an
+      // extension[2].
+      // [1] [6.0:319:1-2]
+      // [2] [6.0:319:36-37]
+      auto pp{propertyListParser(extParser)};
+      return OmpTraitSelector(std::move(*name), std::move(*pp.Parse(state)));
+    }
+
+    llvm_unreachable("Unhandled trait name?");
+  }
+
+private:
+  const Parser<OmpTraitSelectorName> np;
+};
 
-TYPE_PARSER(sourced(construct<OmpTraitSelector>( //
-    Parser<OmpTraitSelectorName>{}, //
-    maybe(parenthesized(Parser<OmpTraitSelector::Properties>{})))))
+TYPE_PARSER(sourced(construct<OmpTraitSelector>(
+    sourced(TraitSelectorParser(Parser<OmpTraitSelectorName>{})))))
 
 TYPE_PARSER(construct<OmpTraitSetSelectorName::Value>(
-    "CONSTRUCT" >> pure(OmpTraitSetSelectorName::Value::Construct) ||
-    "DEVICE" >> pure(OmpTraitSetSelectorName::Value::Device) ||
-    "IMPLEMENTATION" >> pure(OmpTraitSetSelectorName::Value::Implementation) ||
-    "TARGET_DEVICE" >> pure(OmpTraitSetSelectorName::Value::Target_Device) ||
-    "USER" >> pure(OmpTraitSetSelectorName::Value::User)))
+    "CONSTRUCT"_id >> pure(OmpTraitSetSelectorName::Value::Construct) ||
+    "DEVICE"_id >> pure(OmpTraitSetSelectorName::Value::Device) ||
+    "IMPLEMENTATION"_id >>
+        pure(OmpTraitSetSelectorName::Value::Implementation) ||
+    "TARGET_DEVICE"_id >> pure(OmpTraitSetSelectorName::Value::Target_Device) ||
+    "USER"_id >> pure(OmpTraitSetSelectorName::Value::User)))
 
 TYPE_PARSER(sourced(construct<OmpTraitSetSelectorName>(
     Parser<OmpTraitSetSelectorName::Value>{})))
 
 TYPE_PARSER(sourced(construct<OmpTraitSetSelector>( //
     Parser<OmpTraitSetSelectorName>{},
-    "=" >> braced(nonemptySeparated(Parser<OmpTraitSelector>{}, ","_tok)))))
+    "=" >> braced(nonemptySeparated(Parser<OmpTraitSelector>{}, ",")))))
 
 TYPE_PARSER(sourced(construct<OmpContextSelectorSpecification>(
-    nonemptySeparated(Parser<OmpTraitSetSelector>{}, ","_tok))))
+    nonemptySeparated(Parser<OmpTraitSetSelector>{}, ","))))
 
 // Parser<OmpContextSelector> == Parser<traits::OmpContextSelectorSpecification>
 
diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
index 7bf404bba2c3e..af5259e1daec4 100644
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -2075,10 +2075,11 @@ class UnparseVisitor {
     Walk(x.v);
     Put(")");
   }
-  void Unparse(const OmpTraitPropertyExtension &x) {
+  void Unparse(const OmpTraitPropertyExtension::Complex &x) {
+    using PropList = std::list<common::Indirection<OmpTraitPropertyExtension>>;
     Walk(std::get<OmpTraitPropertyName>(x.t));
     Put("(");
-    Walk(std::get<OmpTraitPropertyExtension::ExtensionList>(x.t), ",");
+    Walk(std::get<PropList>(x.t), ",");
     Put(")");
   }
   void Unparse(const OmpTraitSelector &x) {