diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index eca1c2c1874..4724a5f00e2 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -16135,9 +16135,9 @@ namespace ts {
                 ) {
                     const privateIdentifierDescription = unmatchedProperty.valueDeclaration.name.escapedText;
                     const symbolTableKey = getSymbolNameForPrivateIdentifier(source.symbol, privateIdentifierDescription);
-                    if (symbolTableKey && !!getPropertyOfType(source, symbolTableKey)) {
+                    if (symbolTableKey && getPropertyOfType(source, symbolTableKey)) {
                         const sourceName = source.symbol.valueDeclaration.name;
-                        const targetName = isClassDeclaration(target.symbol.valueDeclaration) ? target.symbol.valueDeclaration.name : undefined;
+                        const targetName = target.symbol.valueDeclaration && isClassDeclaration(target.symbol.valueDeclaration) ? target.symbol.valueDeclaration.name : undefined;
                         reportError(
                             Diagnostics.Property_0_in_type_1_refers_to_a_different_member_that_cannot_be_accessed_from_within_type_2,
                             diagnosticName(privateIdentifierDescription),
diff --git a/tests/baselines/reference/privateNamesUnique-5.errors.txt b/tests/baselines/reference/privateNamesUnique-5.errors.txt
new file mode 100644
index 00000000000..31a6d20b99c
--- /dev/null
+++ b/tests/baselines/reference/privateNamesUnique-5.errors.txt
@@ -0,0 +1,21 @@
+tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts(12,7): error TS2322: Type 'B' is not assignable to type 'A2'.
+  Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type '(anonymous)'.
+
+
+==== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts (1 errors) ====
+    // same as privateNamesUnique-1, but with an interface
+    
+    class A {
+        #foo: number;
+    }
+    interface A2 extends A { }
+    
+    class B {
+        #foo: number;
+    }
+    
+    const b: A2 = new B();
+          ~
+!!! error TS2322: Type 'B' is not assignable to type 'A2'.
+!!! error TS2322:   Property '#foo' in type 'B' refers to a different member that cannot be accessed from within type '(anonymous)'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/privateNamesUnique-5.js b/tests/baselines/reference/privateNamesUnique-5.js
new file mode 100644
index 00000000000..75d378c1f1d
--- /dev/null
+++ b/tests/baselines/reference/privateNamesUnique-5.js
@@ -0,0 +1,32 @@
+//// [privateNamesUnique-5.ts]
+// same as privateNamesUnique-1, but with an interface
+
+class A {
+    #foo: number;
+}
+interface A2 extends A { }
+
+class B {
+    #foo: number;
+}
+
+const b: A2 = new B();
+
+
+//// [privateNamesUnique-5.js]
+"use strict";
+// same as privateNamesUnique-1, but with an interface
+var _foo, _foo_1;
+class A {
+    constructor() {
+        _foo.set(this, void 0);
+    }
+}
+_foo = new WeakMap();
+class B {
+    constructor() {
+        _foo_1.set(this, void 0);
+    }
+}
+_foo_1 = new WeakMap();
+const b = new B();
diff --git a/tests/baselines/reference/privateNamesUnique-5.symbols b/tests/baselines/reference/privateNamesUnique-5.symbols
new file mode 100644
index 00000000000..ab414f2729b
--- /dev/null
+++ b/tests/baselines/reference/privateNamesUnique-5.symbols
@@ -0,0 +1,25 @@
+=== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts ===
+// same as privateNamesUnique-1, but with an interface
+
+class A {
+>A : Symbol(A, Decl(privateNamesUnique-5.ts, 0, 0))
+
+    #foo: number;
+>#foo : Symbol(A.#foo, Decl(privateNamesUnique-5.ts, 2, 9))
+}
+interface A2 extends A { }
+>A2 : Symbol(A2, Decl(privateNamesUnique-5.ts, 4, 1))
+>A : Symbol(A, Decl(privateNamesUnique-5.ts, 0, 0))
+
+class B {
+>B : Symbol(B, Decl(privateNamesUnique-5.ts, 5, 26))
+
+    #foo: number;
+>#foo : Symbol(B.#foo, Decl(privateNamesUnique-5.ts, 7, 9))
+}
+
+const b: A2 = new B();
+>b : Symbol(b, Decl(privateNamesUnique-5.ts, 11, 5))
+>A2 : Symbol(A2, Decl(privateNamesUnique-5.ts, 4, 1))
+>B : Symbol(B, Decl(privateNamesUnique-5.ts, 5, 26))
+
diff --git a/tests/baselines/reference/privateNamesUnique-5.types b/tests/baselines/reference/privateNamesUnique-5.types
new file mode 100644
index 00000000000..04a3a838c7d
--- /dev/null
+++ b/tests/baselines/reference/privateNamesUnique-5.types
@@ -0,0 +1,23 @@
+=== tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts ===
+// same as privateNamesUnique-1, but with an interface
+
+class A {
+>A : A
+
+    #foo: number;
+>#foo : number
+}
+interface A2 extends A { }
+
+class B {
+>B : B
+
+    #foo: number;
+>#foo : number
+}
+
+const b: A2 = new B();
+>b : A2
+>new B() : B
+>B : typeof B
+
diff --git a/tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts b/tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts
new file mode 100644
index 00000000000..0db3e2c3f6f
--- /dev/null
+++ b/tests/cases/conformance/classes/members/privateNames/privateNamesUnique-5.ts
@@ -0,0 +1,16 @@
+// @strict: true
+// @target: es6
+// @strictPropertyInitialization: false
+
+// same as privateNamesUnique-1, but with an interface
+
+class A {
+    #foo: number;
+}
+interface A2 extends A { }
+
+class B {
+    #foo: number;
+}
+
+const b: A2 = new B();