diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 91f4247a673..3d6db01580a 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -617,6 +617,8 @@ namespace ts {
 
         function isNarrowingBinaryExpression(expr: BinaryExpression) {
             switch (expr.operatorToken.kind) {
+                case SyntaxKind.EqualsToken:
+                    return isNarrowableReference(expr.left);
                 case SyntaxKind.EqualsEqualsToken:
                 case SyntaxKind.ExclamationEqualsToken:
                 case SyntaxKind.EqualsEqualsEqualsToken:
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 195245648a7..a3b3451fe35 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7671,6 +7671,8 @@ namespace ts {
 
             function narrowTypeByBinaryExpression(type: Type, expr: BinaryExpression, assumeTrue: boolean): Type {
                 switch (expr.operatorToken.kind) {
+                    case SyntaxKind.EqualsToken:
+                        return narrowTypeByTruthiness(type, expr.left, assumeTrue);
                     case SyntaxKind.EqualsEqualsToken:
                     case SyntaxKind.ExclamationEqualsToken:
                     case SyntaxKind.EqualsEqualsEqualsToken: