diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 2f020f46f22..76ab92544f4 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -15391,9 +15391,12 @@ namespace ts {
                 }
 
                 if (!targetType) {
-                    const constructSignatures = getSignaturesOfType(rightType, SignatureKind.Construct);
-                    targetType = constructSignatures && constructSignatures.length ?
-                        getUnionType(map(constructSignatures, signature => getReturnTypeOfSignature(getErasedSignature(signature)))) :
+                    let constructSignatures = getSignaturesOfType(rightType, SignatureKind.Construct);
+                    if (constructSignatures.length === 0) {
+                        constructSignatures = filter(getSignaturesOfType(rightType, SignatureKind.Call), sig => isJSConstructor(sig.declaration));
+                    }
+                    targetType = constructSignatures.length ?
+                        getUnionType(map(constructSignatures, signature => isJSConstructor(signature.declaration) && getJSClassType(getSymbolOfNode(signature.declaration!)) || getReturnTypeOfSignature(getErasedSignature(signature)))) :
                         emptyObjectType;
                 }
 
diff --git a/tests/baselines/reference/controlFlowInstanceof.js b/tests/baselines/reference/controlFlowInstanceof.js
deleted file mode 100644
index 1ac63f138f6..00000000000
--- a/tests/baselines/reference/controlFlowInstanceof.js
+++ /dev/null
@@ -1,196 +0,0 @@
-//// [controlFlowInstanceof.ts]
-// Repros from #10167
-
-function f1(s: Set<string> | Set<number>) {
-    s = new Set<number>();
-    s;  // Set<number>
-    if (s instanceof Set) {
-        s;  // Set<number>
-    }
-    s;  // Set<number>
-    s.add(42);
-}
-
-function f2(s: Set<string> | Set<number>) {
-    s = new Set<number>();
-    s;  // Set<number>
-    if (s instanceof Promise) {
-        s;  // Set<number> & Promise<any>
-    }
-    s;  // Set<number>
-    s.add(42);
-}
-
-function f3(s: Set<string> | Set<number>) {
-    s;  // Set<string> | Set<number>
-    if (s instanceof Set) {
-        s;  // Set<string> | Set<number>
-    }
-    else {
-        s;  // never
-    }
-}
-
-function f4(s: Set<string> | Set<number>) {
-    s = new Set<number>();
-    s;  // Set<number>
-    if (s instanceof Set) {
-        s;  // Set<number>
-    }
-    else {
-        s;  // never
-    }
-}
-
-// More tests
-
-class A { a: string }
-class B extends A { b: string }
-class C extends A { c: string }
-
-function foo(x: A | undefined) {
-    x;  // A | undefined
-    if (x instanceof B || x instanceof C) {
-        x;  // B | C
-    }
-    x;  // A | undefined
-    if (x instanceof B && x instanceof C) {
-        x;  // B & C
-    }
-    x;  // A | undefined
-    if (!x) {
-        return;
-    }
-    x;  // A
-    if (x instanceof B) {
-        x;  // B
-        if (x instanceof C) {
-            x;  // B & C
-        }
-        else {
-            x;  // B
-        }
-        x;  // B
-    }
-    else {
-        x;  // A
-    }
-    x;  // A
-}
-
-// X is neither assignable to Y nor a subtype of Y
-// Y is assignable to X, but not a subtype of X
-
-interface X {
-    x?: string;
-}
-
-class Y {
-    y: string;
-}
-
-function goo(x: X) {
-    x;
-    if (x instanceof Y) {
-        x.y;
-    }
-    x;
-}
-
-// Repro from #27282
-
-declare const x: (() => void)|null;
-declare const ctor: Function;
-
-if (x instanceof ctor) {
-    x();
-}
-
-
-//// [controlFlowInstanceof.js]
-// Repros from #10167
-function f1(s) {
-    s = new Set();
-    s; // Set<number>
-    if (s instanceof Set) {
-        s; // Set<number>
-    }
-    s; // Set<number>
-    s.add(42);
-}
-function f2(s) {
-    s = new Set();
-    s; // Set<number>
-    if (s instanceof Promise) {
-        s; // Set<number> & Promise<any>
-    }
-    s; // Set<number>
-    s.add(42);
-}
-function f3(s) {
-    s; // Set<string> | Set<number>
-    if (s instanceof Set) {
-        s; // Set<string> | Set<number>
-    }
-    else {
-        s; // never
-    }
-}
-function f4(s) {
-    s = new Set();
-    s; // Set<number>
-    if (s instanceof Set) {
-        s; // Set<number>
-    }
-    else {
-        s; // never
-    }
-}
-// More tests
-class A {
-}
-class B extends A {
-}
-class C extends A {
-}
-function foo(x) {
-    x; // A | undefined
-    if (x instanceof B || x instanceof C) {
-        x; // B | C
-    }
-    x; // A | undefined
-    if (x instanceof B && x instanceof C) {
-        x; // B & C
-    }
-    x; // A | undefined
-    if (!x) {
-        return;
-    }
-    x; // A
-    if (x instanceof B) {
-        x; // B
-        if (x instanceof C) {
-            x; // B & C
-        }
-        else {
-            x; // B
-        }
-        x; // B
-    }
-    else {
-        x; // A
-    }
-    x; // A
-}
-class Y {
-}
-function goo(x) {
-    x;
-    if (x instanceof Y) {
-        x.y;
-    }
-    x;
-}
-if (x instanceof ctor) {
-    x();
-}
diff --git a/tests/baselines/reference/controlFlowInstanceof.symbols b/tests/baselines/reference/controlFlowInstanceof.symbols
index 72ab32d29d5..2be43d5ef6e 100644
--- a/tests/baselines/reference/controlFlowInstanceof.symbols
+++ b/tests/baselines/reference/controlFlowInstanceof.symbols
@@ -247,3 +247,28 @@ if (x instanceof ctor) {
 >x : Symbol(x, Decl(controlFlowInstanceof.ts, 100, 13))
 }
 
+// Repro from #27550 (based on uglify code)
+=== tests/cases/compiler/uglify.js ===
+/** @constructor */
+function AtTop(val) { this.val = val }
+>AtTop : Symbol(AtTop, Decl(uglify.js, 0, 0))
+>val : Symbol(val, Decl(uglify.js, 1, 15))
+>this.val : Symbol(AtTop.val, Decl(uglify.js, 1, 21))
+>this : Symbol(AtTop, Decl(uglify.js, 0, 0))
+>val : Symbol(AtTop.val, Decl(uglify.js, 1, 21))
+>val : Symbol(val, Decl(uglify.js, 1, 15))
+
+/** @type {*} */
+var v = 1;
+>v : Symbol(v, Decl(uglify.js, 3, 3))
+
+if (v instanceof AtTop) {
+>v : Symbol(v, Decl(uglify.js, 3, 3))
+>AtTop : Symbol(AtTop, Decl(uglify.js, 0, 0))
+
+    v.val
+>v.val : Symbol(AtTop.val, Decl(uglify.js, 1, 21))
+>v : Symbol(v, Decl(uglify.js, 3, 3))
+>val : Symbol(AtTop.val, Decl(uglify.js, 1, 21))
+}
+
diff --git a/tests/baselines/reference/controlFlowInstanceof.types b/tests/baselines/reference/controlFlowInstanceof.types
index e7c05a4c015..9aa38025a1c 100644
--- a/tests/baselines/reference/controlFlowInstanceof.types
+++ b/tests/baselines/reference/controlFlowInstanceof.types
@@ -261,3 +261,31 @@ if (x instanceof ctor) {
 >x : () => void
 }
 
+// Repro from #27550 (based on uglify code)
+=== tests/cases/compiler/uglify.js ===
+/** @constructor */
+function AtTop(val) { this.val = val }
+>AtTop : typeof AtTop
+>val : any
+>this.val = val : any
+>this.val : any
+>this : AtTop
+>val : any
+>val : any
+
+/** @type {*} */
+var v = 1;
+>v : any
+>1 : 1
+
+if (v instanceof AtTop) {
+>v instanceof AtTop : boolean
+>v : any
+>AtTop : typeof AtTop
+
+    v.val
+>v.val : any
+>v : AtTop
+>val : any
+}
+
diff --git a/tests/cases/compiler/controlFlowInstanceof.ts b/tests/cases/compiler/controlFlowInstanceof.ts
index f9cf844572f..b032fb708dc 100644
--- a/tests/cases/compiler/controlFlowInstanceof.ts
+++ b/tests/cases/compiler/controlFlowInstanceof.ts
@@ -1,6 +1,10 @@
 // @target: es6
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
 // @strictNullChecks: true
 
+// @Filename: controlFlowInstanceof.ts
 // Repros from #10167
 
 function f1(s: Set<string> | Set<number>) {
@@ -107,3 +111,13 @@ declare const ctor: Function;
 if (x instanceof ctor) {
     x();
 }
+
+// Repro from #27550 (based on uglify code)
+// @Filename: uglify.js
+/** @constructor */
+function AtTop(val) { this.val = val }
+/** @type {*} */
+var v = 1;
+if (v instanceof AtTop) {
+    v.val
+}