diff --git a/src/ast/nodes/BinaryExpression.ts b/src/ast/nodes/BinaryExpression.ts
index d1167831f79..5e73aa8d715 100644
--- a/src/ast/nodes/BinaryExpression.ts
+++ b/src/ast/nodes/BinaryExpression.ts
@@ -16,8 +16,32 @@ import type * as NodeType from './NodeType';
 import { type LiteralValueOrUnknown, UnknownValue } from './shared/Expression';
 import { type ExpressionNode, NodeBase } from './shared/Node';
 
+type Operator =
+	| '!='
+	| '!=='
+	| '%'
+	| '&'
+	| '*'
+	| '**'
+	| '+'
+	| '-'
+	| '/'
+	| '<'
+	| '<<'
+	| '<='
+	| '=='
+	| '==='
+	| '>'
+	| '>='
+	| '>>'
+	| '>>>'
+	| '^'
+	| '|'
+	| 'in'
+	| 'instanceof';
+
 const binaryOperators: {
-	[operator: string]: (left: LiteralValue, right: LiteralValue) => LiteralValueOrUnknown;
+	[operator in Operator]?: (left: LiteralValue, right: LiteralValue) => LiteralValueOrUnknown;
 } = {
 	'!=': (left, right) => left != right,
 	'!==': (left, right) => left !== right,
@@ -29,15 +53,13 @@ const binaryOperators: {
 	'+': (left: any, right: any) => left + right,
 	'-': (left: any, right: any) => left - right,
 	'/': (left: any, right: any) => left / right,
-	'<': (left, right) => (left as NonNullable<LiteralValue>) < (right as NonNullable<LiteralValue>),
+	'<': (left, right) => left! < right!,
 	'<<': (left: any, right: any) => left << right,
-	'<=': (left, right) =>
-		(left as NonNullable<LiteralValue>) <= (right as NonNullable<LiteralValue>),
+	'<=': (left, right) => left! <= right!,
 	'==': (left, right) => left == right,
 	'===': (left, right) => left === right,
-	'>': (left, right) => (left as NonNullable<LiteralValue>) > (right as NonNullable<LiteralValue>),
-	'>=': (left, right) =>
-		(left as NonNullable<LiteralValue>) >= (right as NonNullable<LiteralValue>),
+	'>': (left, right) => left! > right!,
+	'>=': (left, right) => left! >= right!,
 	'>>': (left: any, right: any) => left >> right,
 	'>>>': (left: any, right: any) => left >>> right,
 	'^': (left: any, right: any) => left ^ right,
@@ -79,8 +101,9 @@ export default class BinaryExpression extends NodeBase implements DeoptimizableE
 			this.operator === '+' &&
 			this.parent instanceof ExpressionStatement &&
 			this.left.getLiteralValueAtPath(EMPTY_PATH, SHARED_RECURSION_TRACKER, this) === ''
-		)
+		) {
 			return true;
+		}
 		return super.hasEffects(context);
 	}
 
diff --git a/src/ast/nodes/NewExpression.ts b/src/ast/nodes/NewExpression.ts
index e12915475e5..974a357bc2c 100644
--- a/src/ast/nodes/NewExpression.ts
+++ b/src/ast/nodes/NewExpression.ts
@@ -28,8 +28,9 @@ export default class NewExpression extends NodeBase {
 			if (
 				(this.context.options.treeshake as NormalizedTreeshakingOptions).annotations &&
 				this.annotations
-			)
+			) {
 				return false;
+			}
 			return (
 				this.callee.hasEffects(context) ||
 				this.callee.hasEffectsOnInteractionAtPath(EMPTY_PATH, this.interaction, context)
diff --git a/test/function/samples/instanceof/left-hand-effect/_config.js b/test/function/samples/instanceof/left-hand-effect/_config.js
new file mode 100644
index 00000000000..edadb884deb
--- /dev/null
+++ b/test/function/samples/instanceof/left-hand-effect/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'retains side effects in the left hand side of instanceof'
+};
diff --git a/test/function/samples/instanceof/left-hand-effect/main.js b/test/function/samples/instanceof/left-hand-effect/main.js
new file mode 100644
index 00000000000..f29fbed86a7
--- /dev/null
+++ b/test/function/samples/instanceof/left-hand-effect/main.js
@@ -0,0 +1,14 @@
+let effect = false;
+
+class Bar {}
+class Foo {
+	constructor() {
+		effect = true;
+	}
+}
+
+if (new Foo() instanceof Bar) {
+	assert.fail('Wrong instance relation');
+}
+
+assert.ok(effect);
diff --git a/test/function/samples/instanceof/right-hand-effect/_config.js b/test/function/samples/instanceof/right-hand-effect/_config.js
new file mode 100644
index 00000000000..466922bcd67
--- /dev/null
+++ b/test/function/samples/instanceof/right-hand-effect/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'retains side effects in the right hand side of instanceof'
+};
diff --git a/test/function/samples/instanceof/right-hand-effect/main.js b/test/function/samples/instanceof/right-hand-effect/main.js
new file mode 100644
index 00000000000..01fa8698a53
--- /dev/null
+++ b/test/function/samples/instanceof/right-hand-effect/main.js
@@ -0,0 +1,14 @@
+let effect = false;
+
+class Foo {}
+
+if (
+	new Foo() instanceof
+	class {
+		[(effect = true)]() {}
+	}
+) {
+	assert.fail('Wrong instance relation');
+}
+
+assert.ok(effect);
diff --git a/test/function/samples/instanceof/used-parameter/_config.js b/test/function/samples/instanceof/used-parameter/_config.js
new file mode 100644
index 00000000000..1312a923985
--- /dev/null
+++ b/test/function/samples/instanceof/used-parameter/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'retains instanceof for function parameters'
+};
diff --git a/test/function/samples/instanceof/used-parameter/main.js b/test/function/samples/instanceof/used-parameter/main.js
new file mode 100644
index 00000000000..61c8724c78d
--- /dev/null
+++ b/test/function/samples/instanceof/used-parameter/main.js
@@ -0,0 +1,12 @@
+let effect = false;
+
+class Foo {}
+
+function checkInstance(instance) {
+	if (instance instanceof Foo) {
+		effect = true;
+	}
+}
+
+checkInstance(new Foo());
+assert.ok(effect);
diff --git a/test/function/samples/instanceof/used/_config.js b/test/function/samples/instanceof/used/_config.js
new file mode 100644
index 00000000000..fe5faa35411
--- /dev/null
+++ b/test/function/samples/instanceof/used/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'retains instanceof if it is true'
+};
diff --git a/test/function/samples/instanceof/used/main.js b/test/function/samples/instanceof/used/main.js
new file mode 100644
index 00000000000..cbd5feb2583
--- /dev/null
+++ b/test/function/samples/instanceof/used/main.js
@@ -0,0 +1,5 @@
+class Foo {}
+
+if (!(new Foo() instanceof Foo)) {
+	assert.fail('instanceof not resolved correctly');
+}