microsoft · Andarist · Feb 11, 2026
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -17965,7 +17965,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (type.flags & TypeFlags.Any) {
                     addElement(type, ElementFlags.Rest, target.labeledElementDeclarations?.[i]);
                 }
-                else if (type.flags & TypeFlags.InstantiableNonPrimitive || isGenericMappedType(type)) {
+                else if (someContainedType(type, t => !!(t.flags & TypeFlags.InstantiableNonPrimitive) || isGenericMappedType(type))) {
                     // Generic variadic elements stay as they are.
                     addElement(type, ElementFlags.Variadic, target.labeledElementDeclarations?.[i]);
                 }
@@ -28515,6 +28515,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return type.flags & TypeFlags.Union ? every((type as UnionType).types, f) : f(type);
     }
 
+    function someContainedType(type: Type, f: (t: Type) => boolean): boolean {
+        return type.flags & TypeFlags.UnionOrIntersection ? some((type as UnionOrIntersectionType).types, f) : f(type);
+    }
+
     function everyContainedType(type: Type, f: (t: Type) => boolean): boolean {
         return type.flags & TypeFlags.UnionOrIntersection ? every((type as UnionOrIntersectionType).types, f) : f(type);
     }

diff --git a/tests/baselines/reference/recursiveConditionalCrash5.errors.txt b/tests/baselines/reference/recursiveConditionalCrash5.errors.txt
@@ -0,0 +1,10 @@
+recursiveConditionalCrash5.ts(3,60): error TS2589: Type instantiation is excessively deep and possibly infinite.
+
+
+==== recursiveConditionalCrash5.ts (1 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/63040
+
+    type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;
+                                                               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
+
diff --git a/tests/baselines/reference/recursiveConditionalCrash5.symbols b/tests/baselines/reference/recursiveConditionalCrash5.symbols
@@ -0,0 +1,13 @@
+//// [tests/cases/compiler/recursiveConditionalCrash5.ts] ////
+
+=== recursiveConditionalCrash5.ts ===
+// https://github.com/microsoft/TypeScript/issues/63040
+
+type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;
+>StringTreeArrayAsTuple : Symbol(StringTreeArrayAsTuple, Decl(recursiveConditionalCrash5.ts, 0, 0))
+>T : Symbol(T, Decl(recursiveConditionalCrash5.ts, 2, 28))
+>T : Symbol(T, Decl(recursiveConditionalCrash5.ts, 2, 28))
+>R : Symbol(R, Decl(recursiveConditionalCrash5.ts, 2, 53))
+>StringTreeArrayAsTuple : Symbol(StringTreeArrayAsTuple, Decl(recursiveConditionalCrash5.ts, 0, 0))
+>R : Symbol(R, Decl(recursiveConditionalCrash5.ts, 2, 53))
+
diff --git a/tests/baselines/reference/recursiveConditionalCrash5.types b/tests/baselines/reference/recursiveConditionalCrash5.types
@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/recursiveConditionalCrash5.ts] ////
+
+=== recursiveConditionalCrash5.ts ===
+// https://github.com/microsoft/TypeScript/issues/63040
+
+type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;
+>StringTreeArrayAsTuple : StringTreeArrayAsTuple<T>
+>                       : ^^^^^^^^^^^^^^^^^^^^^^^^^
+
diff --git a/tests/cases/compiler/recursiveConditionalCrash5.ts b/tests/cases/compiler/recursiveConditionalCrash5.ts
@@ -0,0 +1,6 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/63040
+
+type StringTreeArrayAsTuple<T> = (T extends [...infer R] ? [...StringTreeArrayAsTuple<R>] : never) & boolean;