diff --git a/src/compile/data.ts b/src/compile/data.ts
index b73cf7d94d2..757b9038599 100644
--- a/src/compile/data.ts
+++ b/src/compile/data.ts
@@ -816,7 +816,7 @@ export namespace stackScale {
     const child = model.child();
     const childDataComponent = child.component.data;
 
-    // If child doesn't have its own data source, but have stack scale source, then merge
+    // If child doesn't have its own data source, but has stack scale source, then merge
     if (!childDataComponent.source && childDataComponent.stackScale) {
       let stackComponent = childDataComponent.stackScale;
 
diff --git a/src/compile/layer.ts b/src/compile/layer.ts
index e9ebf377928..bf04fa9f766 100644
--- a/src/compile/layer.ts
+++ b/src/compile/layer.ts
@@ -104,13 +104,13 @@ export class LayerModel extends Model {
               if (isArray(childScales.main.domain)) {
                 modelScales.main.domain = modelDomain.concat(childDomain);
               } else {
-                model.addWarning('scales cannot be unioned with explicit domain');
+                model.addWarning('custom domain scale cannot be unioned with default field-based domain');
               }
             } else {
               const unionedFields = isUnionedDomain(modelDomain) ? modelDomain.fields : [modelDomain] as VgDataRef[];
 
               if (isArray(childDomain)) {
-                model.addWarning('scales cannot be unioned with explicit domain');
+                model.addWarning('custom domain scale cannot be unioned with default field-based domain');
               }
 
               let fields = isDataRefDomain(childDomain) ? unionedFields.concat([childDomain]) :