diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 8acecf57e5..69862a93d2 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7693,6 +7693,8 @@ namespace ts {
                 return type;
             }
             // In the following we resolve T[K] to the type of the property in T selected by K.
+            // We treat boolean as different from other unions to improve errors;
+            // skipping straight to getPropertyTypeForIndexType gives errors with 'boolean' instead of 'true'.
             const apparentObjectType = getApparentType(objectType);
             if (indexType.flags & TypeFlags.Union && !(indexType.flags & TypeFlags.Boolean)) {
                 const propTypes: Type[] = [];