diff --git a/lib/vast/Conversion/Parser/Refine.cpp b/lib/vast/Conversion/Parser/Refine.cpp
index fae07eb16e..4b4faf63c5 100644
--- a/lib/vast/Conversion/Parser/Refine.cpp
+++ b/lib/vast/Conversion/Parser/Refine.cpp
@@ -107,6 +107,64 @@ namespace vast::conv {
             }
         };
 
+        struct RefineDeclType : operation_conversion_pattern< pr::Decl >
+        {
+            using op_t = pr::Decl;
+            using base = operation_conversion_pattern< op_t >;
+            using base::base;
+
+            using adaptor_t = typename op_t::Adaptor;
+
+            static mlir_type resolve(mlir_type a, mlir_type b) {
+                if (!a) {
+                    return b;
+                }
+                return a == b ? a : pr::MaybeDataType::get(a.getContext());
+            }
+
+            static mlir_type assigned_type(mlir_value value) {
+                if (!value.getDefiningOp()) {
+                    return value.getType();
+                } else if (auto cast = dyn_cast< pr::Cast >(value.getDefiningOp())) {
+                    return assigned_type(cast.getOperand());
+                } else {
+                    return value.getType();
+                }
+            }
+
+            static mlir_type assigned_type(op_t op) {
+                mlir_type type = {};
+                auto mod       = op->template getParentOfType< core::ModuleOp >();
+                for (auto use : core::symbol_table::get_symbol_uses(op, mod)) {
+                    if (auto ref = dyn_cast< pr::Ref >(use.getUser())) {
+                        for (auto ref_user : ref->getUsers()) {
+                            if (auto assign = dyn_cast< pr::Assign >(ref_user)) {
+                                type = resolve(type, assigned_type(assign.getValue()));
+                            } else if (isa< mlir::CallOpInterface >(ref_user)) {
+                                return op.getType();
+                            }
+                        }
+                    }
+                }
+                return op.getType();
+            }
+
+            logical_result matchAndRewrite(
+                op_t op, adaptor_t adaptor, conversion_rewriter &rewriter
+            ) const override {
+                op->dump();
+                rewriter.modifyOpInPlace(op, [&] { op.setType(assigned_type(op)); });
+                return mlir::success();
+            }
+
+            static void legalize(base_conversion_config &cfg) {
+                cfg.target.addDynamicallyLegalOp< op_t >([](op_t op) {
+                    return !pr::is_maybedata(op.getType())
+                        || pr::is_maybedata(assigned_type(op));
+                });
+            }
+        };
+
         template< typename op_t >
         struct DeadOpElimination : operation_conversion_pattern< op_t >
         {
@@ -144,6 +202,7 @@ namespace vast::conv {
             NoParseFold< hl::ChooseExprOp >,
             NoParseFold< hl::BinaryCondOp >,
             RefineReturn,
+            RefineDeclType,
             DefinitionElimination< hl::EnumDeclOp >,
             DefinitionElimination< hl::StructDeclOp >,
             DefinitionElimination< hl::UnionDeclOp >,