diff --git a/src/codegen/expressions/method-calls.ts b/src/codegen/expressions/method-calls.ts
index 68fa970f..15f25812 100644
--- a/src/codegen/expressions/method-calls.ts
+++ b/src/codegen/expressions/method-calls.ts
@@ -1043,7 +1043,10 @@ export class MethodCallGenerator {
             imp.source.startsWith("../") ||
             imp.source.startsWith("/");
           if (!isRelative && imp.specifiers && imp.specifiers.indexOf(varName) !== -1) {
-            return "null";
+            return this.ctx.emitError(
+              `'${varName}.${method}()' — module '${imp.source}' is not supported by ChadScript`,
+              expr.loc,
+            );
           }
         }
       }