diff --git a/packages/abi-to-sol/src/solidity.ts b/packages/abi-to-sol/src/solidity.ts
index 3095f84..0ebd7cf 100644
--- a/packages/abi-to-sol/src/solidity.ts
+++ b/packages/abi-to-sol/src/solidity.ts
@@ -463,18 +463,23 @@ class SolidityGenerator implements Visitor<string, Context | undefined> {
     kind: Kind,
     context: Pick<Context, "interfaceName"> = {}
   ): string {
-    if (
-      this.versionsFeatures["user-defined-value-types"].supported() &&
-      Kind.isUserDefinedValueType(kind)
-    ) {
-      if (
+    if (Kind.isUserDefinedValueType(kind)) {
+      const result = (
         kind.identifier.container &&
         kind.identifier.container.name !== context.interfaceName
-      ) {
-        return `${kind.identifier.container.name}.${kind.identifier.name}`;
+      )
+        ? `${kind.identifier.container.name}.${kind.identifier.name}`
+        : kind.identifier.name;
+
+      if (!this.versionsFeatures["user-defined-value-types"].supported()) {
+        return [
+          `/* warning: missing UDVT support in source Solidity version; `,
+          `parameter is \`${result}\`. */ `,
+          kind.type
+        ].join("");
       }
 
-      return kind.identifier.name
+      return result;
     }
 
     if (Kind.isElementary(kind)) {