diff --git a/flang/lib/Lower/ConvertCall.cpp b/flang/lib/Lower/ConvertCall.cpp
--- a/flang/lib/Lower/ConvertCall.cpp
+++ b/flang/lib/Lower/ConvertCall.cpp
@@ -1345,6 +1345,8 @@
     }
     if (!argLowering) {
       // No argument lowering instruction, lower by value.
+      assert(!arg.value()->handleDynamicOptional() &&
+             "should use genOptionalValue");
       hlfir::Entity actual = arg.value()->getActual(loc, builder);
       operands.emplace_back(
           Fortran::lower::convertToValue(loc, converter, actual, stmtCtx));