diff --git a/flang/include/flang/Parser/dump-parse-tree.h b/flang/include/flang/Parser/dump-parse-tree.h
--- a/flang/include/flang/Parser/dump-parse-tree.h
+++ b/flang/include/flang/Parser/dump-parse-tree.h
@@ -85,6 +85,7 @@
   NODE(parser, AccEndBlockDirective)
   NODE(parser, AccEndCombinedDirective)
   NODE(parser, AccGangArgument)
+  NODE(parser, AccCollapseArg)
   NODE(parser, AccObject)
   NODE(parser, AccObjectList)
   NODE(parser, AccObjectListWithModifier)
diff --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -4097,6 +4097,11 @@
   std::tuple<std::optional<ScalarIntExpr>, std::optional<AccSizeExpr>> t;
 };
 
+struct AccCollapseArg {
+  TUPLE_CLASS_BOILERPLATE(AccCollapseArg);
+  std::tuple<bool, ScalarIntConstantExpr> t;
+};
+
 struct AccClause {
   UNION_CLASS_BOILERPLATE(AccClause);
 
diff --git a/flang/lib/Lower/OpenACC.cpp b/flang/lib/Lower/OpenACC.cpp
--- a/flang/lib/Lower/OpenACC.cpp
+++ b/flang/lib/Lower/OpenACC.cpp
@@ -910,9 +910,16 @@
 
   // Lower clauses mapped to attributes
   for (const Fortran::parser::AccClause &clause : accClauseList.v) {
+    mlir::Location clauseLocation = converter.genLocation(clause.source);
     if (const auto *collapseClause =
             std::get_if<Fortran::parser::AccClause::Collapse>(&clause.u)) {
-      const auto *expr = Fortran::semantics::GetExpr(collapseClause->v);
+      const Fortran::parser::AccCollapseArg &arg = collapseClause->v;
+      const auto &force = std::get<bool>(arg.t);
+      if (force)
+        TODO(clauseLocation, "OpenACC collapse force modifier");
+      const auto &intExpr =
+          std::get<Fortran::parser::ScalarIntConstantExpr>(arg.t);
+      const auto *expr = Fortran::semantics::GetExpr(intExpr);
       const std::optional<int64_t> collapseValue =
           Fortran::evaluate::ToInt64(*expr);
       if (collapseValue) {
diff --git a/flang/lib/Parser/openacc-parsers.cpp b/flang/lib/Parser/openacc-parsers.cpp
--- a/flang/lib/Parser/openacc-parsers.cpp
+++ b/flang/lib/Parser/openacc-parsers.cpp
@@ -72,6 +72,10 @@
     maybe(("NUM:"_tok >> scalarIntExpr || scalarIntExpr)),
     maybe(", STATIC:" >> Parser<AccSizeExpr>{})))
 
+// 2.9.1 collapse
+TYPE_PARSER(construct<AccCollapseArg>(
+    "FORCE:"_tok >> pure(true) || pure(false), scalarIntConstantExpr))
+
 // 2.5.13 Reduction
 // Operator for reduction
 TYPE_PARSER(sourced(construct<AccReductionOperator>(
diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -1912,6 +1912,14 @@
     Walk("NUM:", std::get<std::optional<ScalarIntExpr>>(x.t));
     Walk(", STATIC:", std::get<std::optional<AccSizeExpr>>(x.t));
   }
+  void Unparse(const AccCollapseArg &x) {
+    const auto &force{std::get<bool>(x.t)};
+    const auto &collapseValue{std::get<parser::ScalarIntConstantExpr>(x.t)};
+    if (force) {
+      Put("FORCE:");
+    }
+    Walk(collapseValue);
+  }
   void Unparse(const OpenACCBlockConstruct &x) {
     BeginOpenACC();
     Word("!$ACC ");
diff --git a/flang/lib/Semantics/check-acc-structure.cpp b/flang/lib/Semantics/check-acc-structure.cpp
--- a/flang/lib/Semantics/check-acc-structure.cpp
+++ b/flang/lib/Semantics/check-acc-structure.cpp
@@ -307,8 +307,6 @@
 }
 
 // Clause checkers
-CHECK_REQ_SCALAR_INT_CONSTANT_CLAUSE(Collapse, ACCC_collapse)
-
 CHECK_SIMPLE_CLAUSE(Auto, ACCC_auto)
 CHECK_SIMPLE_CLAUSE(Async, ACCC_async)
 CHECK_SIMPLE_CLAUSE(Attach, ACCC_attach)
@@ -432,6 +430,15 @@
   }
 }
 
+void AccStructureChecker::Enter(const parser::AccClause::Collapse &x) {
+  CheckAllowed(llvm::acc::Clause::ACCC_collapse);
+  const parser::AccCollapseArg &accCollapseArg = x.v;
+  const auto &collapseValue{
+      std::get<parser::ScalarIntConstantExpr>(accCollapseArg.t)};
+  RequiresConstantPositiveParameter(
+      llvm::acc::Clause::ACCC_collapse, collapseValue);
+}
+
 llvm::StringRef AccStructureChecker::getClauseName(llvm::acc::Clause clause) {
   return llvm::acc::getOpenACCClauseName(clause);
 }
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -904,7 +904,9 @@
   for (const auto &clause : x.v) {
     if (const auto *collapseClause{
             std::get_if<parser::AccClause::Collapse>(&clause.u)}) {
-      if (const auto v{EvaluateInt64(context_, collapseClause->v)}) {
+      const parser::AccCollapseArg &arg = collapseClause->v;
+      const auto &collapseValue{std::get<parser::ScalarIntConstantExpr>(arg.t)};
+      if (const auto v{EvaluateInt64(context_, collapseValue)}) {
         collapseLevel = *v;
       }
     }
diff --git a/flang/test/Parser/acc-unparse.f90 b/flang/test/Parser/acc-unparse.f90
--- a/flang/test/Parser/acc-unparse.f90
+++ b/flang/test/Parser/acc-unparse.f90
@@ -17,3 +17,17 @@
 
 !CHECK-LABEL: PROGRAM bug47659
 !CHECK: !$ACC PARALLEL LOOP
+
+
+subroutine acc_loop()
+  integer :: i, j
+
+  !$acc loop collapse(force: 2)
+  do i = 1, 10
+    do j = 1, 10
+    end do
+  end do
+end subroutine
+
+!CHECK-LABEL: SUBROUTINE acc_loop
+!CHECK: !$ACC LOOP COLLAPSE(FORCE:2_4)
diff --git a/llvm/include/llvm/Frontend/OpenACC/ACC.td b/llvm/include/llvm/Frontend/OpenACC/ACC.td
--- a/llvm/include/llvm/Frontend/OpenACC/ACC.td
+++ b/llvm/include/llvm/Frontend/OpenACC/ACC.td
@@ -56,7 +56,7 @@
 
 // 2.9.1
 def ACCC_Collapse : Clause<"collapse"> {
-  let flangClass = "ScalarIntConstantExpr";
+  let flangClass = "AccCollapseArg";
 }
 
 // 2.7.6