diff --git a/flang/lib/Semantics/assignment.cpp b/flang/lib/Semantics/assignment.cpp
index e69a73c7837ce..0b57197fb8db8 100644
--- a/flang/lib/Semantics/assignment.cpp
+++ b/flang/lib/Semantics/assignment.cpp
@@ -66,8 +66,13 @@ void AssignmentContext::Analyze(const parser::AssignmentStmt &stmt) {
     const SomeExpr &rhs{assignment->rhs};
     auto lhsLoc{std::get<parser::Variable>(stmt.t).GetSource()};
     const Scope &scope{context_.FindScope(lhsLoc)};
-    if (auto whyNot{WhyNotDefinable(lhsLoc, scope,
-            DefinabilityFlags{DefinabilityFlag::VectorSubscriptIsOk}, lhs)}) {
+    DefinabilityFlags flags{DefinabilityFlag::VectorSubscriptIsOk};
+    bool isDefinedAssignment{
+        std::holds_alternative<evaluate::ProcedureRef>(assignment->u)};
+    if (isDefinedAssignment) {
+      flags.set(DefinabilityFlag::AllowEventLockOrNotifyType);
+    }
+    if (auto whyNot{WhyNotDefinable(lhsLoc, scope, flags, lhs)}) {
       if (whyNot->IsFatal()) {
         if (auto *msg{Say(lhsLoc,
                 "Left-hand side of assignment is not definable"_err_en_US)}) {
@@ -79,9 +84,7 @@ void AssignmentContext::Analyze(const parser::AssignmentStmt &stmt) {
       }
     }
     auto rhsLoc{std::get<parser::Expr>(stmt.t).source};
-    if (std::holds_alternative<evaluate::ProcedureRef>(assignment->u)) {
-      // it's a defined ASSIGNMENT(=)
-    } else {
+    if (!isDefinedAssignment) {
       CheckForPureContext(rhs, rhsLoc);
     }
     if (whereDepth_ > 0) {
diff --git a/flang/lib/Semantics/check-call.cpp b/flang/lib/Semantics/check-call.cpp
index 597c280a6df8b..8631789b9f526 100644
--- a/flang/lib/Semantics/check-call.cpp
+++ b/flang/lib/Semantics/check-call.cpp
@@ -703,12 +703,14 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
   // Problems with polymorphism are caught in the callee's definition.
   if (scope) {
     std::optional<parser::MessageFixedText> undefinableMessage;
-    if (dummy.intent == common::Intent::Out) {
-      undefinableMessage =
-          "Actual argument associated with INTENT(OUT) %s is not definable"_err_en_US;
-    } else if (dummy.intent == common::Intent::InOut) {
+    DefinabilityFlags flags{DefinabilityFlag::PolymorphicOkInPure};
+    if (dummy.intent == common::Intent::InOut) {
+      flags.set(DefinabilityFlag::AllowEventLockOrNotifyType);
       undefinableMessage =
           "Actual argument associated with INTENT(IN OUT) %s is not definable"_err_en_US;
+    } else if (dummy.intent == common::Intent::Out) {
+      undefinableMessage =
+          "Actual argument associated with INTENT(OUT) %s is not definable"_err_en_US;
     } else if (context.ShouldWarn(common::LanguageFeature::
                        UndefinableAsynchronousOrVolatileActual)) {
       if (dummy.attrs.test(
@@ -722,7 +724,6 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
       }
     }
     if (undefinableMessage) {
-      DefinabilityFlags flags{DefinabilityFlag::PolymorphicOkInPure};
       if (isElemental) { // 15.5.2.4(21)
         flags.set(DefinabilityFlag::VectorSubscriptIsOk);
       }
diff --git a/flang/lib/Semantics/definable.cpp b/flang/lib/Semantics/definable.cpp
index 88f9463e35c78..6d0155c24c31a 100644
--- a/flang/lib/Semantics/definable.cpp
+++ b/flang/lib/Semantics/definable.cpp
@@ -204,7 +204,8 @@ static std::optional<parser::Message> WhyNotDefinableLast(parser::CharBlock at,
     }
     return std::nullopt; // pointer assignment - skip following checks
   }
-  if (IsOrContainsEventOrLockComponent(ultimate)) {
+  if (!flags.test(DefinabilityFlag::AllowEventLockOrNotifyType) &&
+      IsOrContainsEventOrLockComponent(ultimate)) {
     return BlameSymbol(at,
         "'%s' is an entity with either an EVENT_TYPE or LOCK_TYPE"_en_US,
         original);
diff --git a/flang/lib/Semantics/definable.h b/flang/lib/Semantics/definable.h
index 709bbba494d10..902702dbccbf3 100644
--- a/flang/lib/Semantics/definable.h
+++ b/flang/lib/Semantics/definable.h
@@ -32,7 +32,8 @@ ENUM_CLASS(DefinabilityFlag,
     AcceptAllocatable, // treat allocatable as if it were a pointer
     SourcedAllocation, // ALLOCATE(a,SOURCE=)
     PolymorphicOkInPure, // don't check for polymorphic type in pure subprogram
-    DoNotNoteDefinition) // context does not imply definition
+    DoNotNoteDefinition, // context does not imply definition
+    AllowEventLockOrNotifyType)
 
 using DefinabilityFlags =
     common::EnumSet<DefinabilityFlag, DefinabilityFlag_enumSize>;
diff --git a/flang/test/Semantics/definable01.f90 b/flang/test/Semantics/definable01.f90
index ff71b419fa971..d3b31ee38b2a3 100644
--- a/flang/test/Semantics/definable01.f90
+++ b/flang/test/Semantics/definable01.f90
@@ -109,7 +109,29 @@ pure function test6(lp)
   end
   pure subroutine test7(lp)
     type(list), pointer :: lp
-    !CHECK-NOT: error:
-    lp%next%next => null()
+    lp%next%next => null() ! ok
   end
 end module
+program main
+  use iso_fortran_env, only: lock_type
+  type(lock_type) lock
+  interface
+    subroutine inlock(lock)
+      import lock_type
+      type(lock_type), intent(in) :: lock
+    end
+    subroutine outlock(lock)
+      import lock_type
+      !CHECK: error: An INTENT(OUT) dummy argument may not be, or contain, EVENT_TYPE or LOCK_TYPE
+      type(lock_type), intent(out) :: lock
+    end
+    subroutine inoutlock(lock)
+      import lock_type
+      type(lock_type), intent(in out) :: lock
+    end
+  end interface
+  call inlock(lock) ! ok
+  call inoutlock(lock) ! ok
+  !CHECK: error: Actual argument associated with INTENT(OUT) dummy argument 'lock=' is not definable
+  call outlock(lock)
+end