@@ -15583,7 +15583,7 @@ namespace ts {
                         }
                     }
                     if (unionParent && !result && targetIsOptional) {
-                        result = isRelatedTo(source, undefinedType);
+                        result = isRelatedTo(source, addOptionality(getTypeOfSymbol(targetProp), targetIsOptional));
                     }
                     if (unionParent && !result && reportErrors) {
                         // The easiest way to get the right errors here is to un-defer (which may be costly)
Original file line number	Diff line number	Diff line change
`@@ -15583,7 +15583,7 @@ namespace ts {`
`15583`	`15583`	`}`
`15584`	`15584`	`}`
`15585`	`15585`	`if (unionParent && !result && targetIsOptional) {`
`15586`		`- result = isRelatedTo(source, undefinedType);`
	`15586`	`+ result = isRelatedTo(source, addOptionality(getTypeOfSymbol(targetProp), targetIsOptional));`
`15587`	`15587`	`}`
`15588`	`15588`	`if (unionParent && !result && reportErrors) {`
`15589`	`15589`	`// The easiest way to get the right errors here is to un-defer (which may be costly)`