Index: flang/lib/Semantics/check-omp-structure.h
===================================================================
--- flang/lib/Semantics/check-omp-structure.h
+++ flang/lib/Semantics/check-omp-structure.h
@@ -166,7 +166,7 @@
 private:
   bool HasInvalidWorksharingNesting(
       const parser::CharBlock &, const OmpDirectiveSet &);
-
+  bool IsCloselyNested(const OmpDirectiveSet &set);
   // specific clause related
   bool ScheduleModifierHasType(const parser::OmpScheduleClause &,
       const parser::OmpScheduleModifierType::ModType &);
Index: flang/lib/Semantics/check-omp-structure.cpp
===================================================================
--- flang/lib/Semantics/check-omp-structure.cpp
+++ flang/lib/Semantics/check-omp-structure.cpp
@@ -127,11 +127,69 @@
   std::map<std::string, std::int64_t> labelNamesandLevels_;
 };
 
+bool OmpStructureChecker::IsCloselyNested(const OmpDirectiveSet &set) {
+  // Definition of close nesting:
+  //
+  // `A region nested inside another region with no parallel region nested
+  // between them`
+  //
+  // Examples:
+  //   non-parallel construct 1
+  //    non-parallel construct 2
+  //      parallel construct
+  //        construct 3
+  // In the above example, construct 3 is NOT closely nested inside construct 1
+  // or 2
+  //
+  //   non-parallel construct 1
+  //    non-parallel construct 2
+  //        construct 3
+  // In the above example, construct 3 is closely nested inside BOTH construct 1
+  // and 2
+  //
+  // Algorithm:
+  //  Check at each level of the context stack, whether we have a violating
+  //  directive.  If such a level is found, traverse until the deepest level
+  //  to see if we found any `parallel` construct during our travel.
+  //  If found, the `close nesting` definition is violated under the starting
+  //  level, we resume the same check from the level just below the found level
+  //  of the parallel construct.
+  //
+  //  If at any level, we find a violating directive AND there is no `parallel`
+  //  construct found between that starting level and the deepest level,
+  //  definition of `close nesting` is satisfied.
+  if (CurrentDirectiveIsNested()) {
+    for (unsigned int i = 0; i < dirContext_.size() - 1; i++) {
+      if (set.test(dirContext_[i].directive)) {
+        // Found the starting level of a violating construct
+        // Check if we can find a `parallel` construct in between
+        bool foundPar = false;
+        for (unsigned int j = i + 1; j < dirContext_.size(); j++) {
+          if (llvm::omp::parallelSet.test(dirContext_[j].directive)) {
+            // Found parallel, means NOT closely nested, resume the
+            // check from the next level
+            foundPar = true;
+            i = j + 1;
+            break;
+          }
+        }
+        if (!foundPar) {
+          // We found a violating directive at the i-th level and
+          // we did not find a `parallel` starting from i+1-th level
+          // until the deepest level.  Means it is closely nested.
+          return true;
+        }
+      }
+    }
+  }
+  return false;
+}
+
 bool OmpStructureChecker::HasInvalidWorksharingNesting(
     const parser::CharBlock &source, const OmpDirectiveSet &set) {
   // set contains all the invalid closely nested directives
   // for the given directive (`source` here)
-  if (CurrentDirectiveIsNested() && set.test(GetContextParent().directive)) {
+  if (IsCloselyNested(set)) {
     context_.Say(source,
         "A worksharing region may not be closely nested inside a "
         "worksharing, explicit task, taskloop, critical, ordered, atomic, or "
Index: flang/test/Semantics/omp-do05.f90
===================================================================
--- flang/test/Semantics/omp-do05.f90
+++ flang/test/Semantics/omp-do05.f90
@@ -6,7 +6,7 @@
 program omp_do
 
   integer n
-  integer i,j
+  integer i,j,k
   !$omp do
   do i=1,10
     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
@@ -18,6 +18,65 @@
   end do
   !$omp end do
 
+  !$omp do
+  do i=1,10
+    !$omp task
+    do j=1,10
+      !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+      !$omp single
+      do k=1,10
+        print *,"hello"
+      end do
+      !$omp end single
+    end do
+    !$omp end task
+  end do
+  !$omp end do
+
+  !$omp do
+  do i=1,10
+    !$omp parallel
+    do j=1,10
+      !$omp single
+      do k=1,10
+        print *,"hello"
+      end do
+      !$omp end single
+    end do
+    !$omp end parallel
+  end do
+  !$omp end do
+
+!$omp do
+do i=1,10
+  !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+  !$omp single
+  do j=1,10
+    !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+    !$omp single
+    do k=1,10
+      print *,"hello"
+    end do
+    !$omp end single
+  end do
+  !$omp end single
+
+  !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+  !$omp single
+    do k=1,10
+      print *,"hello"
+    end do
+  !$omp end single
+
+  !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+  !$omp do
+    do k=1,10
+      print *,"hello"
+    end do
+  !$omp end do
+end do
+!$omp end do
+
   !$omp parallel default(shared)
   !$omp do
   do i = 1, n
@@ -29,4 +88,19 @@
   !$omp end do
   !$omp end parallel
 
+  !$omp parallel default(shared)
+  !$omp do
+  do i = 1, n
+    !$omp task
+    do j=1,10
+      !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+      !$omp single
+      call work(i, 1)
+      !$omp end single
+    end do
+    !$omp end task
+  end do
+  !$omp end do
+  !$omp end parallel
+
 end program omp_do
Index: flang/test/Semantics/omp-nested01.f90
===================================================================
--- flang/test/Semantics/omp-nested01.f90
+++ flang/test/Semantics/omp-nested01.f90
@@ -11,4 +11,30 @@
         a = 3.14
      enddo
   enddo
+
+  !$omp do
+  do i = 1, N
+   !$omp target
+   do k = 1,N
+     !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+     !$omp do
+     do j = 1, N
+        a = 3.14
+     enddo
+   enddo
+   !$omp end target
+  enddo
+  
+
+  !$omp do
+  do i = 1, N
+   !$omp parallel
+   do k = 1,N
+     !$omp do
+     do j = 1, N
+        a = 3.14
+     enddo
+   enddo
+   !$omp end parallel
+  enddo
 end
Index: flang/test/Semantics/omp-reduction07.f90
===================================================================
--- flang/test/Semantics/omp-reduction07.f90
+++ flang/test/Semantics/omp-reduction07.f90
@@ -54,6 +54,19 @@
   !$omp end do
 !$omp end sections
 
+!$omp sections private(k)
+  !$omp target
+  do j = 1,10
+    !ERROR: A worksharing region may not be closely nested inside a worksharing, explicit task, taskloop, critical, ordered, atomic, or master region
+    !$omp do reduction(+:k) reduction(max:j)
+    do i = 1, 10
+      k = k + 1
+    end do
+    !$omp end do
+  end do
+  !$omp end target
+!$omp end sections
+
 !$omp parallel reduction(+:a)
 !ERROR: REDUCTION variable 'a' is REDUCTION in outer context must be shared in the parallel regions to which any of the worksharing regions arising from the worksharing construct bind.
 !$omp sections reduction(-:a)