diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt b/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
index 5b749df2cab36..9ebf28f1857e9 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
@@ -219,4 +219,13 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
         let x: Array<string>[K] = 'abc';
         let y: ReadonlyArray<string>[K] = 'abc';
     }
+    
+    // Repro from #31439
+    
+    export class c {
+      [x: string]: string;
+      constructor() {
+        this["a"] = "b";
+      }
+    }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.js b/tests/baselines/reference/keyofAndIndexedAccess2.js
index 7bf53b9fba491..374b13b5a643a 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.js
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.js
@@ -136,6 +136,15 @@ function fn4<K extends number>() {
     let x: Array<string>[K] = 'abc';
     let y: ReadonlyArray<string>[K] = 'abc';
 }
+
+// Repro from #31439
+
+export class c {
+  [x: string]: string;
+  constructor() {
+    this["a"] = "b";
+  }
+}
 
 
 //// [keyofAndIndexedAccess2.js]
@@ -226,3 +235,9 @@ function fn4() {
     let x = 'abc';
     let y = 'abc';
 }
+// Repro from #31439
+export class c {
+    constructor() {
+        this["a"] = "b";
+    }
+}
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.symbols b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
index 2155451ef7497..a3412e8a47d31 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
@@ -503,3 +503,17 @@ function fn4<K extends number>() {
 >K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
 }
 
+// Repro from #31439
+
+export class c {
+>c : Symbol(c, Decl(keyofAndIndexedAccess2.ts, 136, 1))
+
+  [x: string]: string;
+>x : Symbol(x, Decl(keyofAndIndexedAccess2.ts, 141, 3))
+
+  constructor() {
+    this["a"] = "b";
+>this : Symbol(c, Decl(keyofAndIndexedAccess2.ts, 136, 1))
+  }
+}
+
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.types b/tests/baselines/reference/keyofAndIndexedAccess2.types
index af43ed0f4eb27..b7b71ba4f9f71 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.types
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.types
@@ -499,3 +499,21 @@ function fn4<K extends number>() {
 >'abc' : "abc"
 }
 
+// Repro from #31439
+
+export class c {
+>c : c
+
+  [x: string]: string;
+>x : string
+
+  constructor() {
+    this["a"] = "b";
+>this["a"] = "b" : "b"
+>this["a"] : string
+>this : this
+>"a" : "a"
+>"b" : "b"
+  }
+}
+