diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 2e0f1ef628101..42ca22e26e588 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2533,10 +2533,12 @@ namespace ts {
 
         /* Starting from 'initial' node walk up the parent chain until 'stopAt' node is reached.
          * If at any point current node is equal to 'parent' node - return true.
+         * If current node is an IIFE, continue walking up.
          * Return false if 'stopAt' node is reached or isFunctionLike(current) === true.
          */
         function isSameScopeDescendentOf(initial: Node, parent: Node | undefined, stopAt: Node): boolean {
-            return !!parent && !!findAncestor(initial, n => n === stopAt || isFunctionLike(n) ? "quit" : n === parent);
+            return !!parent && !!findAncestor(initial, n => n === parent
+                || (n === stopAt || isFunctionLike(n) && !getImmediatelyInvokedFunctionExpression(n) ? "quit" : false));
         }
 
         function getAnyImportSyntax(node: Node): AnyImportSyntax | undefined {
diff --git a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.errors.txt b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.errors.txt
index 91bd5dde00cb6..9dacd0975bd53 100644
--- a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.errors.txt
+++ b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.errors.txt
@@ -2,9 +2,12 @@ tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(2,13): error TS2448: Bl
 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(58,20): error TS2448: Block-scoped variable 'x' used before its declaration.
 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(65,20): error TS2448: Block-scoped variable 'x' used before its declaration.
 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(100,12): error TS2448: Block-scoped variable 'x' used before its declaration.
+tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(111,28): error TS2448: Block-scoped variable 'a' used before its declaration.
+tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(112,21): error TS2448: Block-scoped variable 'a' used before its declaration.
+tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(122,22): error TS2448: Block-scoped variable 'a' used before its declaration.
 
 
-==== tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts (4 errors) ====
+==== tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts (7 errors) ====
     function foo0() {
         let a = x;
                 ~
@@ -120,4 +123,33 @@ tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(100,12): error TS2448:
         }
         let x
     }
+    
+    function foo15() {
+        // https://github.com/microsoft/TypeScript/issues/42678
+        const [
+            a,
+            b,
+        ] = ((): [number, number] => {
+            (() => console.log(a))();  // should error
+                               ~
+!!! error TS2448: Block-scoped variable 'a' used before its declaration.
+!!! related TS2728 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts:108:9: 'a' is declared here.
+            console.log(a);            // should error
+                        ~
+!!! error TS2448: Block-scoped variable 'a' used before its declaration.
+!!! related TS2728 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts:108:9: 'a' is declared here.
+            const b = () => a;         // should be ok
+            return [
+                0,
+                0,
+            ];
+        })();    
+    }
+    
+    function foo16() {
+        let [a] = (() => a)();
+                         ~
+!!! error TS2448: Block-scoped variable 'a' used before its declaration.
+!!! related TS2728 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts:122:10: 'a' is declared here.
+    }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.js b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.js
index 9ca3f8998a2eb..b49ce9ddaa4b2 100644
--- a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.js
+++ b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.js
@@ -102,6 +102,26 @@ function foo14() {
     }
     let x
 }
+
+function foo15() {
+    // https://github.com/microsoft/TypeScript/issues/42678
+    const [
+        a,
+        b,
+    ] = ((): [number, number] => {
+        (() => console.log(a))();  // should error
+        console.log(a);            // should error
+        const b = () => a;         // should be ok
+        return [
+            0,
+            0,
+        ];
+    })();    
+}
+
+function foo16() {
+    let [a] = (() => a)();
+}
 
 
 //// [blockScopedVariablesUseBeforeDef.js]
@@ -219,3 +239,18 @@ function foo14() {
     };
     var x;
 }
+function foo15() {
+    // https://github.com/microsoft/TypeScript/issues/42678
+    var _a = (function () {
+        (function () { return console.log(a); })(); // should error
+        console.log(a); // should error
+        var b = function () { return a; }; // should be ok
+        return [
+            0,
+            0,
+        ];
+    })(), a = _a[0], b = _a[1];
+}
+function foo16() {
+    var a = (function () { return a; })()[0];
+}
diff --git a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.symbols b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.symbols
index 83cb91db1d0cd..ea588cd22fa19 100644
--- a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.symbols
+++ b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.symbols
@@ -213,3 +213,46 @@ function foo14() {
 >x : Symbol(x, Decl(blockScopedVariablesUseBeforeDef.ts, 101, 7))
 }
 
+function foo15() {
+>foo15 : Symbol(foo15, Decl(blockScopedVariablesUseBeforeDef.ts, 102, 1))
+
+    // https://github.com/microsoft/TypeScript/issues/42678
+    const [
+        a,
+>a : Symbol(a, Decl(blockScopedVariablesUseBeforeDef.ts, 106, 11))
+
+        b,
+>b : Symbol(b, Decl(blockScopedVariablesUseBeforeDef.ts, 107, 10))
+
+    ] = ((): [number, number] => {
+        (() => console.log(a))();  // should error
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>a : Symbol(a, Decl(blockScopedVariablesUseBeforeDef.ts, 106, 11))
+
+        console.log(a);            // should error
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>a : Symbol(a, Decl(blockScopedVariablesUseBeforeDef.ts, 106, 11))
+
+        const b = () => a;         // should be ok
+>b : Symbol(b, Decl(blockScopedVariablesUseBeforeDef.ts, 112, 13))
+>a : Symbol(a, Decl(blockScopedVariablesUseBeforeDef.ts, 106, 11))
+
+        return [
+            0,
+            0,
+        ];
+    })();    
+}
+
+function foo16() {
+>foo16 : Symbol(foo16, Decl(blockScopedVariablesUseBeforeDef.ts, 118, 1))
+
+    let [a] = (() => a)();
+>a : Symbol(a, Decl(blockScopedVariablesUseBeforeDef.ts, 121, 9))
+>a : Symbol(a, Decl(blockScopedVariablesUseBeforeDef.ts, 121, 9))
+}
+
diff --git a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.types b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.types
index 3098b8c0f91e0..e24197911cf04 100644
--- a/tests/baselines/reference/blockScopedVariablesUseBeforeDef.types
+++ b/tests/baselines/reference/blockScopedVariablesUseBeforeDef.types
@@ -225,3 +225,65 @@ function foo14() {
 >x : any
 }
 
+function foo15() {
+>foo15 : () => void
+
+    // https://github.com/microsoft/TypeScript/issues/42678
+    const [
+        a,
+>a : number
+
+        b,
+>b : number
+
+    ] = ((): [number, number] => {
+>((): [number, number] => {        (() => console.log(a))();  // should error        console.log(a);            // should error        const b = () => a;         // should be ok        return [            0,            0,        ];    })() : [number, number]
+>((): [number, number] => {        (() => console.log(a))();  // should error        console.log(a);            // should error        const b = () => a;         // should be ok        return [            0,            0,        ];    }) : () => [number, number]
+>(): [number, number] => {        (() => console.log(a))();  // should error        console.log(a);            // should error        const b = () => a;         // should be ok        return [            0,            0,        ];    } : () => [number, number]
+
+        (() => console.log(a))();  // should error
+>(() => console.log(a))() : void
+>(() => console.log(a)) : () => void
+>() => console.log(a) : () => void
+>console.log(a) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>a : number
+
+        console.log(a);            // should error
+>console.log(a) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>a : number
+
+        const b = () => a;         // should be ok
+>b : () => number
+>() => a : () => number
+>a : number
+
+        return [
+>[            0,            0,        ] : [number, number]
+
+            0,
+>0 : 0
+
+            0,
+>0 : 0
+
+        ];
+    })();    
+}
+
+function foo16() {
+>foo16 : () => void
+
+    let [a] = (() => a)();
+>a : any
+>(() => a)() : any
+>(() => a) : () => any
+>() => a : () => any
+>a : any
+}
+
diff --git a/tests/baselines/reference/tryCatchFinallyControlFlow.errors.txt b/tests/baselines/reference/tryCatchFinallyControlFlow.errors.txt
index a6972d05d8ec5..79578f9144de1 100644
--- a/tests/baselines/reference/tryCatchFinallyControlFlow.errors.txt
+++ b/tests/baselines/reference/tryCatchFinallyControlFlow.errors.txt
@@ -2,10 +2,11 @@ tests/cases/compiler/tryCatchFinallyControlFlow.ts(105,5): error TS7027: Unreach
 tests/cases/compiler/tryCatchFinallyControlFlow.ts(118,9): error TS7027: Unreachable code detected.
 tests/cases/compiler/tryCatchFinallyControlFlow.ts(218,13): error TS7027: Unreachable code detected.
 tests/cases/compiler/tryCatchFinallyControlFlow.ts(220,9): error TS7027: Unreachable code detected.
+tests/cases/compiler/tryCatchFinallyControlFlow.ts(255,9): error TS2448: Block-scoped variable 'x' used before its declaration.
 tests/cases/compiler/tryCatchFinallyControlFlow.ts(255,9): error TS7027: Unreachable code detected.
 
 
-==== tests/cases/compiler/tryCatchFinallyControlFlow.ts (5 errors) ====
+==== tests/cases/compiler/tryCatchFinallyControlFlow.ts (6 errors) ====
     // Repro from #34797
     
     function f1() {
@@ -270,6 +271,9 @@ tests/cases/compiler/tryCatchFinallyControlFlow.ts(255,9): error TS7027: Unreach
                 return null;
             }
             x;  // Unreachable
+            ~
+!!! error TS2448: Block-scoped variable 'x' used before its declaration.
+!!! related TS2728 tests/cases/compiler/tryCatchFinallyControlFlow.ts:248:11: 'x' is declared here.
             ~~
 !!! error TS7027: Unreachable code detected.
         })();
diff --git a/tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts b/tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts
index 351bdde122e1c..2e0b0727895d0 100644
--- a/tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts
+++ b/tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts
@@ -102,3 +102,23 @@ function foo14() {
     }
     let x
 }
+
+function foo15() {
+    // https://github.com/microsoft/TypeScript/issues/42678
+    const [
+        a,
+        b,
+    ] = ((): [number, number] => {
+        (() => console.log(a))();  // should error
+        console.log(a);            // should error
+        const b = () => a;         // should be ok
+        return [
+            0,
+            0,
+        ];
+    })();    
+}
+
+function foo16() {
+    let [a] = (() => a)();
+}