diff --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -1532,6 +1532,16 @@
               }
             }
           },
+          [&](const parser::Expr::DefinedUnary &) {
+              context_.Say(expr.source,
+                  "User defined operator not allowed in"
+                  " OpenMP ATOMIC (UPDATE) statement"_err_en_US); 
+          },
+          [&](const parser::Expr::DefinedBinary &) {
+              context_.Say(expr.source,
+                  "User defined operator not allowed in"
+                  " OpenMP ATOMIC (UPDATE) statement"_err_en_US);
+          },
           [&](const auto &x) {
             if (!IsOperatorValid(x, var)) {
               context_.Say(expr.source,
diff --git a/flang/test/Semantics/OpenMP/omp-atomic-user-defined-operators.f90 b/flang/test/Semantics/OpenMP/omp-atomic-user-defined-operators.f90
new file mode 100644
--- /dev/null
+++ b/flang/test/Semantics/OpenMP/omp-atomic-user-defined-operators.f90
@@ -0,0 +1,57 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1 -fopenmp
+! Semantics checks on user defined operators on atomic update statement
+
+module overload_asterisk
+    implicit none
+    private
+    public operator (*)
+
+    interface operator(*)
+        module procedure logical_and
+    end interface
+
+contains
+    pure logical function logical_and(log1, log2)
+        logical, intent(in) :: log1, log2
+
+        logical_and = (log1 .and. log2)
+    end function
+end module
+
+module new_operator
+    implicit none
+    private
+    public operator(.MYOPERATOR.)
+
+    interface operator(.MYOPERATOR.)
+       module procedure myprocedure
+    end interface
+contains
+    pure integer function myprocedure(param1, param2)
+        integer, intent(in) :: param1, param2
+        myprocedure = param1 + param2
+    end function
+end module
+
+program sample
+    use omp_lib
+    use overload_asterisk
+    use new_operator
+    implicit none
+
+    logical  :: T = .true., F = .false.
+    integer :: x, y 
+    !$omp atomic
+        T = T*T
+    
+    !$omp atomic update
+        x = x / y
+     
+    !$omp atomic update
+    !ERROR: User defined operator not allowed in OpenMP ATOMIC (UPDATE) statement
+        x = x .MYOPERATOR. y
+
+    !$omp atomic
+    !ERROR: User defined operator not allowed in OpenMP ATOMIC (UPDATE) statement
+        x = x .MYOPERATOR. y
+end program