diff --git a/packages/forms/src/model.ts b/packages/forms/src/model.ts
index 5433a430d8..c5952f2fe3 100644
--- a/packages/forms/src/model.ts
+++ b/packages/forms/src/model.ts
@@ -1457,7 +1457,9 @@ export class FormGroup extends AbstractControl {
   /**
    * Add a control to this group.
    *
-   * This method also updates the value and validity of the control.
+   * If a control with a given name already exists, it would *not* be replaced with a new one.
+   * If you want to replace an existing control, use the {@link FormGroup#setControl setControl}
+   * method instead. This method also updates the value and validity of the control.
    *
    * @param name The control name to add to the collection
    * @param control Provides the control for the given name
@@ -1495,6 +1497,8 @@ export class FormGroup extends AbstractControl {
   /**
    * Replace an existing control.
    *
+   * If a control with a given name does not exist in this `FormGroup`, it will be added.
+   *
    * @param name The control name to replace in the collection
    * @param control Provides the control for the given name
    * @param options Specifies whether this FormGroup instance should emit events after an