diff --git a/flang/include/flang/Evaluate/tools.h b/flang/include/flang/Evaluate/tools.h
--- a/flang/include/flang/Evaluate/tools.h
+++ b/flang/include/flang/Evaluate/tools.h
@@ -889,6 +889,10 @@
       semantics::Attrs{semantics::Attr::POINTER, semantics::Attr::ALLOCATABLE});
 }
 
+// Like IsAllocatableOrPointer, but accepts pointer function results as being
+// pointers.
+bool IsAllocatableOrPointerObject(const Expr<SomeType> &, FoldingContext &);
+
 // Procedure and pointer detection predicates
 bool IsProcedure(const Expr<SomeType> &);
 bool IsFunction(const Expr<SomeType> &);
@@ -897,6 +901,10 @@
 bool IsNullPointer(const Expr<SomeType> &);
 bool IsObjectPointer(const Expr<SomeType> &, FoldingContext &);
 
+// Can Expr be passed as absent to an optional dummy argument.
+// See 15.5.2.12 point 1 for more details.
+bool MayBePassedAsAbsentOptional(const Expr<SomeType> &, FoldingContext &);
+
 // Extracts the chain of symbols from a designator, which has perhaps been
 // wrapped in an Expr<>, removing all of the (co)subscripts.  The
 // base object will be the first symbol in the result vector.
diff --git a/flang/lib/Evaluate/fold-complex.cpp b/flang/lib/Evaluate/fold-complex.cpp
--- a/flang/lib/Evaluate/fold-complex.cpp
+++ b/flang/lib/Evaluate/fold-complex.cpp
@@ -41,6 +41,15 @@
         // CMPLX(X [, KIND]) with complex X
         return Fold(context, ConvertToType<T>(std::move(*x)));
       } else {
+        if (args.size() >= 2 && args[1].has_value()) {
+          // Do not fold CMPLX with an Y argument that may be absent at runtime
+          // into a complex constructor so that lowering can deal with the
+          // optional aspect (there is no optional aspect with the complex
+          // constructor).
+          if (MayBePassedAsAbsentOptional(*args[1]->UnwrapExpr(), context)) {
+            return Expr<T>{std::move(funcRef)};
+          }
+        }
         // CMPLX(X [, Y [, KIND]]) with non-complex X
         Expr<SomeType> re{std::move(*args[0].value().UnwrapExpr())};
         Expr<SomeType> im{args.size() >= 2 && args[1].has_value()
diff --git a/flang/lib/Evaluate/tools.cpp b/flang/lib/Evaluate/tools.cpp
--- a/flang/lib/Evaluate/tools.cpp
+++ b/flang/lib/Evaluate/tools.cpp
@@ -1078,6 +1078,24 @@
   return std::nullopt;
 }
 
+bool IsAllocatableOrPointerObject(
+    const Expr<SomeType> &expr, FoldingContext &context) {
+  const semantics::Symbol *sym{UnwrapWholeSymbolOrComponentDataRef(expr)};
+  return (sym && semantics::IsAllocatableOrPointer(*sym)) ||
+      evaluate::IsObjectPointer(expr, context);
+}
+
+bool MayBePassedAsAbsentOptional(
+    const Expr<SomeType> &expr, FoldingContext &context) {
+  const semantics::Symbol *sym{UnwrapWholeSymbolOrComponentDataRef(expr)};
+  // 15.5.2.12 1. is pretty clear that an unallocated allocatable/pointer actual
+  // may be passed to a non-allocatable/non-pointer optional dummy. Note that
+  // other compilers (like nag, nvfortran, ifort, gfortran and xlf) seems to
+  // ignore this point in intrinsic contexts (e.g CMPLX argument).
+  return (sym && semantics::IsOptional(*sym)) ||
+      IsAllocatableOrPointerObject(expr, context);
+}
+
 } // namespace Fortran::evaluate
 
 namespace Fortran::semantics {