diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 8305443a19bac..5814b2dcfbf42 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20192,7 +20192,7 @@ namespace ts {
                 markAliasReferenced(parentSymbol, node);
             }
             if (!prop) {
-                const indexInfo = assignmentKind === AssignmentKind.None || !isGenericObjectType(leftType) ? getIndexInfoOfType(apparentType, IndexKind.String) : undefined;
+                const indexInfo = assignmentKind === AssignmentKind.None || !isGenericObjectType(leftType) || isThisTypeParameter(leftType) ? getIndexInfoOfType(apparentType, IndexKind.String) : undefined;
                 if (!(indexInfo && indexInfo.type)) {
                     if (isJSLiteralType(leftType)) {
                         return anyType;
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt b/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
index 40ccd13dac4eb..fffeac41ff7b5 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.errors.txt
@@ -222,11 +222,12 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
         let y: ReadonlyArray<string>[K] = 'abc';
     }
     
-    // Repro from #31439
+    // Repro from #31439 and #31691
     
     export class c {
       [x: string]: string;
       constructor() {
+        this.a = "b";
         this["a"] = "b";
       }
     }
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.js b/tests/baselines/reference/keyofAndIndexedAccess2.js
index 7547a3f84c593..91cf2c89ff24b 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.js
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.js
@@ -137,11 +137,12 @@ function fn4<K extends number>() {
     let y: ReadonlyArray<string>[K] = 'abc';
 }
 
-// Repro from #31439
+// Repro from #31439 and #31691
 
 export class c {
   [x: string]: string;
   constructor() {
+    this.a = "b";
     this["a"] = "b";
   }
 }
@@ -245,9 +246,10 @@ function fn4() {
     let x = 'abc';
     let y = 'abc';
 }
-// Repro from #31439
+// Repro from #31439 and #31691
 export class c {
     constructor() {
+        this.a = "b";
         this["a"] = "b";
     }
 }
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.symbols b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
index 91602f93e1d85..4a7721ff801a0 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.symbols
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.symbols
@@ -503,7 +503,7 @@ function fn4<K extends number>() {
 >K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
 }
 
-// Repro from #31439
+// Repro from #31439 and #31691
 
 export class c {
 >c : Symbol(c, Decl(keyofAndIndexedAccess2.ts, 136, 1))
@@ -512,6 +512,9 @@ export class c {
 >x : Symbol(x, Decl(keyofAndIndexedAccess2.ts, 141, 3))
 
   constructor() {
+    this.a = "b";
+>this : Symbol(c, Decl(keyofAndIndexedAccess2.ts, 136, 1))
+
     this["a"] = "b";
 >this : Symbol(c, Decl(keyofAndIndexedAccess2.ts, 136, 1))
   }
@@ -520,44 +523,44 @@ export class c {
 // Repro from #31385
 
 type Foo<T> = { [key: string]: { [K in keyof T]: K }[keyof T] };
->Foo : Symbol(Foo, Decl(keyofAndIndexedAccess2.ts, 145, 1))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 149, 9))
->key : Symbol(key, Decl(keyofAndIndexedAccess2.ts, 149, 17))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 149, 34))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 149, 9))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 149, 34))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 149, 9))
+>Foo : Symbol(Foo, Decl(keyofAndIndexedAccess2.ts, 146, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 150, 9))
+>key : Symbol(key, Decl(keyofAndIndexedAccess2.ts, 150, 17))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 150, 34))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 150, 9))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 150, 34))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 150, 9))
 
 type Bar<T> = { [key: string]: { [K in keyof T]: [K] }[keyof T] };
->Bar : Symbol(Bar, Decl(keyofAndIndexedAccess2.ts, 149, 64))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 151, 9))
->key : Symbol(key, Decl(keyofAndIndexedAccess2.ts, 151, 17))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 151, 34))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 151, 9))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 151, 34))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 151, 9))
+>Bar : Symbol(Bar, Decl(keyofAndIndexedAccess2.ts, 150, 64))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 152, 9))
+>key : Symbol(key, Decl(keyofAndIndexedAccess2.ts, 152, 17))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 152, 34))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 152, 9))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 152, 34))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 152, 9))
 
 type Baz<T, Q extends Foo<T>> = { [K in keyof Q]: T[Q[K]] };
->Baz : Symbol(Baz, Decl(keyofAndIndexedAccess2.ts, 151, 66))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 153, 9))
->Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 153, 11))
->Foo : Symbol(Foo, Decl(keyofAndIndexedAccess2.ts, 145, 1))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 153, 9))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 153, 35))
->Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 153, 11))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 153, 9))
->Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 153, 11))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 153, 35))
+>Baz : Symbol(Baz, Decl(keyofAndIndexedAccess2.ts, 152, 66))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 154, 9))
+>Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 154, 11))
+>Foo : Symbol(Foo, Decl(keyofAndIndexedAccess2.ts, 146, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 154, 9))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 154, 35))
+>Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 154, 11))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 154, 9))
+>Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 154, 11))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 154, 35))
 
 type Qux<T, Q extends Bar<T>> = { [K in keyof Q]: T[Q[K]["0"]] };
->Qux : Symbol(Qux, Decl(keyofAndIndexedAccess2.ts, 153, 60))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 155, 9))
->Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 155, 11))
->Bar : Symbol(Bar, Decl(keyofAndIndexedAccess2.ts, 149, 64))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 155, 9))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 155, 35))
->Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 155, 11))
->T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 155, 9))
->Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 155, 11))
->K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 155, 35))
+>Qux : Symbol(Qux, Decl(keyofAndIndexedAccess2.ts, 154, 60))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 156, 9))
+>Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 156, 11))
+>Bar : Symbol(Bar, Decl(keyofAndIndexedAccess2.ts, 150, 64))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 156, 9))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 156, 35))
+>Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 156, 11))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 156, 9))
+>Q : Symbol(Q, Decl(keyofAndIndexedAccess2.ts, 156, 11))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 156, 35))
 
diff --git a/tests/baselines/reference/keyofAndIndexedAccess2.types b/tests/baselines/reference/keyofAndIndexedAccess2.types
index 45cf1d4bad5d4..a6d8315466562 100644
--- a/tests/baselines/reference/keyofAndIndexedAccess2.types
+++ b/tests/baselines/reference/keyofAndIndexedAccess2.types
@@ -499,7 +499,7 @@ function fn4<K extends number>() {
 >'abc' : "abc"
 }
 
-// Repro from #31439
+// Repro from #31439 and #31691
 
 export class c {
 >c : c
@@ -508,6 +508,13 @@ export class c {
 >x : string
 
   constructor() {
+    this.a = "b";
+>this.a = "b" : "b"
+>this.a : string
+>this : this
+>a : string
+>"b" : "b"
+
     this["a"] = "b";
 >this["a"] = "b" : "b"
 >this["a"] : string
diff --git a/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts b/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts
index 898648cea44fe..b242aa3de60bc 100644
--- a/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts
+++ b/tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts
@@ -139,11 +139,12 @@ function fn4<K extends number>() {
     let y: ReadonlyArray<string>[K] = 'abc';
 }
 
-// Repro from #31439
+// Repro from #31439 and #31691
 
 export class c {
   [x: string]: string;
   constructor() {
+    this.a = "b";
     this["a"] = "b";
   }
 }