diff --git a/flang/include/flang/Parser/dump-parse-tree.h b/flang/include/flang/Parser/dump-parse-tree.h
index bfeb23de53539..675faeb33668f 100644
--- a/flang/include/flang/Parser/dump-parse-tree.h
+++ b/flang/include/flang/Parser/dump-parse-tree.h
@@ -177,6 +177,7 @@ class ParseTreeDumper {
   NODE(parser, Call)
   NODE(parser, CallStmt)
   NODE(CallStmt, Chevrons)
+  NODE(CallStmt, StarOrExpr)
   NODE(parser, CaseConstruct)
   NODE(CaseConstruct, Case)
   NODE(parser, CaseSelector)
diff --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
index d2c5b45d99581..37991739026b5 100644
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -3247,13 +3247,14 @@ struct FunctionReference {
 
 // R1521 call-stmt -> CALL procedure-designator [ chevrons ]
 //         [( [actual-arg-spec-list] )]
-// (CUDA) chevrons -> <<< scalar-expr, scalar-expr [,
+// (CUDA) chevrons -> <<< * | scalar-expr, scalar-expr [,
 //          scalar-int-expr [, scalar-int-expr ] ] >>>
 struct CallStmt {
   BOILERPLATE(CallStmt);
+  WRAPPER_CLASS(StarOrExpr, std::optional<ScalarExpr>);
   struct Chevrons {
     TUPLE_CLASS_BOILERPLATE(Chevrons);
-    std::tuple<ScalarExpr, ScalarExpr, std::optional<ScalarIntExpr>,
+    std::tuple<StarOrExpr, ScalarExpr, std::optional<ScalarIntExpr>,
         std::optional<ScalarIntExpr>>
         t;
   };
diff --git a/flang/lib/Parser/program-parsers.cpp b/flang/lib/Parser/program-parsers.cpp
index 2b7da18a09bb3..e365cd24a6aed 100644
--- a/flang/lib/Parser/program-parsers.cpp
+++ b/flang/lib/Parser/program-parsers.cpp
@@ -474,10 +474,13 @@ TYPE_CONTEXT_PARSER("function reference"_en_US,
 
 // R1521 call-stmt -> CALL procedure-designator [chevrons]
 ///                          [( [actual-arg-spec-list] )]
-// (CUDA) chevrons -> <<< scalar-expr, scalar-expr [, scalar-int-expr
+// (CUDA) chevrons -> <<< * | scalar-expr, scalar-expr [, scalar-int-expr
 //                      [, scalar-int-expr ] ] >>>
+constexpr auto starOrExpr{
+    construct<CallStmt::StarOrExpr>("*" >> pure<std::optional<ScalarExpr>>() ||
+        applyFunction(presentOptional<ScalarExpr>, scalarExpr))};
 TYPE_PARSER(extension<LanguageFeature::CUDA>(
-    "<<<" >> construct<CallStmt::Chevrons>(scalarExpr, "," >> scalarExpr,
+    "<<<" >> construct<CallStmt::Chevrons>(starOrExpr, ", " >> scalarExpr,
                  maybe("," >> scalarIntExpr), maybe("," >> scalarIntExpr)) /
         ">>>"))
 constexpr auto actualArgSpecList{optionalList(actualArgSpec)};
diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
index bbb126dcdb6d5..5d70f3433b445 100644
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -1703,6 +1703,13 @@ class UnparseVisitor {
   void Unparse(const IntrinsicStmt &x) { // R1519
     Word("INTRINSIC :: "), Walk(x.v, ", ");
   }
+  void Unparse(const CallStmt::StarOrExpr &x) {
+    if (x.v) {
+      Walk(*x.v);
+    } else {
+      Word("*");
+    }
+  }
   void Unparse(const CallStmt::Chevrons &x) { // CUDA
     Walk(std::get<0>(x.t)); // grid
     Word(","), Walk(std::get<1>(x.t)); // block
diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index c70c8a8aecc2f..ead9982112678 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -3066,11 +3066,17 @@ std::optional<Chevrons> ExpressionAnalyzer::AnalyzeChevrons(
     return false;
   }};
   if (const auto &chevrons{call.chevrons}) {
-    if (auto expr{Analyze(std::get<0>(chevrons->t))};
-        expr && checkLaunchArg(*expr, "grid")) {
-      result.emplace_back(*expr);
+    auto &starOrExpr{std::get<0>(chevrons->t)};
+    if (starOrExpr.v) {
+      if (auto expr{Analyze(*starOrExpr.v)};
+          expr && checkLaunchArg(*expr, "grid")) {
+        result.emplace_back(*expr);
+      } else {
+        return std::nullopt;
+      }
     } else {
-      return std::nullopt;
+      result.emplace_back(
+          AsGenericExpr(evaluate::Constant<evaluate::CInteger>{-1}));
     }
     if (auto expr{Analyze(std::get<1>(chevrons->t))};
         expr && checkLaunchArg(*expr, "block")) {
diff --git a/flang/test/Parser/cuf-sanity-common b/flang/test/Parser/cuf-sanity-common
index 9341f054d79d4..7005ef07b2265 100644
--- a/flang/test/Parser/cuf-sanity-common
+++ b/flang/test/Parser/cuf-sanity-common
@@ -40,6 +40,7 @@ module m
     call globalsub<<<1, 2>>>
     call globalsub<<<1, 2, 3>>>
     call globalsub<<<1, 2, 3, 4>>>
+    call globalsub<<<*,5>>>
     allocate(pa(32), pinned = isPinned)
   end subroutine
 end module
diff --git a/flang/test/Parser/cuf-sanity-tree.CUF b/flang/test/Parser/cuf-sanity-tree.CUF
index 2820441d5b5f0..a8b2f93913ca9 100644
--- a/flang/test/Parser/cuf-sanity-tree.CUF
+++ b/flang/test/Parser/cuf-sanity-tree.CUF
@@ -166,7 +166,7 @@ include "cuf-sanity-common"
 !CHECK: | | | | | Call
 !CHECK: | | | | | | ProcedureDesignator -> Name = 'globalsub'
 !CHECK: | | | | | Chevrons
-!CHECK: | | | | | | Scalar -> Expr = '1_4'
+!CHECK: | | | | | | StarOrExpr -> Scalar -> Expr = '1_4'
 !CHECK: | | | | | | | LiteralConstant -> IntLiteralConstant = '1'
 !CHECK: | | | | | | Scalar -> Expr = '2_4'
 !CHECK: | | | | | | | LiteralConstant -> IntLiteralConstant = '2'
@@ -174,7 +174,7 @@ include "cuf-sanity-common"
 !CHECK: | | | | | Call
 !CHECK: | | | | | | ProcedureDesignator -> Name = 'globalsub'
 !CHECK: | | | | | Chevrons
-!CHECK: | | | | | | Scalar -> Expr = '1_4'
+!CHECK: | | | | | | StarOrExpr -> Scalar -> Expr = '1_4'
 !CHECK: | | | | | | | LiteralConstant -> IntLiteralConstant = '1'
 !CHECK: | | | | | | Scalar -> Expr = '2_4'
 !CHECK: | | | | | | | LiteralConstant -> IntLiteralConstant = '2'
@@ -184,7 +184,7 @@ include "cuf-sanity-common"
 !CHECK: | | | | | Call
 !CHECK: | | | | | | ProcedureDesignator -> Name = 'globalsub'
 !CHECK: | | | | | Chevrons
-!CHECK: | | | | | | Scalar -> Expr = '1_4'
+!CHECK: | | | | | | StarOrExpr -> Scalar -> Expr = '1_4'
 !CHECK: | | | | | | | LiteralConstant -> IntLiteralConstant = '1'
 !CHECK: | | | | | | Scalar -> Expr = '2_4'
 !CHECK: | | | | | | | LiteralConstant -> IntLiteralConstant = '2'
diff --git a/flang/test/Parser/cuf-sanity-unparse.CUF b/flang/test/Parser/cuf-sanity-unparse.CUF
index d4be347dd044e..2e2df9ac6646a 100644
--- a/flang/test/Parser/cuf-sanity-unparse.CUF
+++ b/flang/test/Parser/cuf-sanity-unparse.CUF
@@ -43,6 +43,7 @@ include "cuf-sanity-common"
 !CHECK:    CALL globalsub<<<1_4,2_4>>>()
 !CHECK:    CALL globalsub<<<1_4,2_4,3_4>>>()
 !CHECK:    CALL globalsub<<<1_4,2_4,3_4,4_4>>>()
+!CHECK:    CALL globalsub<<<-1_4,5_4>>>()
 !CHECK:   ALLOCATE(pa(32_4), PINNED=ispinned)
 !CHECK:  END SUBROUTINE
 !CHECK: END MODULE