diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 6e7c99a04de19..8e47a5ea3fbc4 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -34621,15 +34621,17 @@ namespace ts {
             }
 
             function checkNaNEquality(errorNode: Node | undefined, operator: SyntaxKind, left: Expression, right: Expression, leftType: Type, rightType: Type) {
-                const isLeftNaN = leftType.flags & TypeFlags.Number && isNaN(skipParentheses(left));
-                const isRightNaN = rightType.flags & TypeFlags.Number && isNaN(skipParentheses(right));
+                const isLeftNaN = (leftType.flags & TypeFlags.Number) && isNaN(skipParentheses(left));
+                const isRightNaN = (rightType.flags & TypeFlags.Number) && isNaN(skipParentheses(right));
                 if (isLeftNaN || isRightNaN) {
                     const err = error(errorNode, Diagnostics.This_condition_will_always_return_0,
                         tokenToString(operator === SyntaxKind.EqualsEqualsEqualsToken || operator === SyntaxKind.EqualsEqualsToken ? SyntaxKind.FalseKeyword : SyntaxKind.TrueKeyword));
                     if (isLeftNaN && isRightNaN) return;
+                    const operatorString = operator === SyntaxKind.ExclamationEqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsToken ? tokenToString(SyntaxKind.ExclamationToken) : "";
                     const location = isLeftNaN ? right : left;
+                    const expression = skipParentheses(location);
                     addRelatedInfo(err, createDiagnosticForNode(location, Diagnostics.Did_you_mean_0,
-                        `${operator === SyntaxKind.ExclamationEqualsEqualsToken || operator === SyntaxKind.ExclamationEqualsToken ? tokenToString(SyntaxKind.ExclamationToken) : ""}Number.isNaN(${getTextOfNode(location)})`));
+                        `${operatorString}Number.isNaN(${isEntityNameExpression(expression) ? entityNameToString(expression) : "..."})`));
                 }
             }
 
diff --git a/tests/baselines/reference/nanEquality.errors.txt b/tests/baselines/reference/nanEquality.errors.txt
index 2c4b78ee66de0..8a47a5be1bd14 100644
--- a/tests/baselines/reference/nanEquality.errors.txt
+++ b/tests/baselines/reference/nanEquality.errors.txt
@@ -1,3 +1,4 @@
+tests/cases/compiler/nanEquality.ts(1,15): error TS2451: Cannot redeclare block-scoped variable 'x'.
 tests/cases/compiler/nanEquality.ts(3,5): error TS2845: This condition will always return 'false'.
 tests/cases/compiler/nanEquality.ts(4,5): error TS2845: This condition will always return 'false'.
 tests/cases/compiler/nanEquality.ts(6,5): error TS2845: This condition will always return 'false'.
@@ -14,10 +15,14 @@ tests/cases/compiler/nanEquality.ts(21,5): error TS2845: This condition will alw
 tests/cases/compiler/nanEquality.ts(22,5): error TS2845: This condition will always return 'true'.
 tests/cases/compiler/nanEquality.ts(24,5): error TS2845: This condition will always return 'false'.
 tests/cases/compiler/nanEquality.ts(25,5): error TS2845: This condition will always return 'true'.
+tests/cases/compiler/nanEquality.ts(28,13): error TS2451: Cannot redeclare block-scoped variable 'x'.
+tests/cases/compiler/nanEquality.ts(29,5): error TS2845: This condition will always return 'false'.
 
 
-==== tests/cases/compiler/nanEquality.ts (16 errors) ====
+==== tests/cases/compiler/nanEquality.ts (19 errors) ====
     declare const x: number;
+                  ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'x'.
     
     if (x === NaN) {}
         ~~~~~~~~~
@@ -86,4 +91,13 @@ tests/cases/compiler/nanEquality.ts(25,5): error TS2845: This condition will alw
     if (NaN != NaN) {}
         ~~~~~~~~~~
 !!! error TS2845: This condition will always return 'true'.
+    
+    // ...
+    declare let x: any;
+                ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'x'.
+    if (NaN === x[0][1]) {}
+        ~~~~~~~~~~~~~~~
+!!! error TS2845: This condition will always return 'false'.
+!!! related TS1369 tests/cases/compiler/nanEquality.ts:29:13: Did you mean 'Number.isNaN(...)'?
     
\ No newline at end of file
diff --git a/tests/baselines/reference/nanEquality.js b/tests/baselines/reference/nanEquality.js
index fd6ebcb39eb0f..25998a55a3c97 100644
--- a/tests/baselines/reference/nanEquality.js
+++ b/tests/baselines/reference/nanEquality.js
@@ -24,6 +24,10 @@ if (NaN !== NaN) {}
 
 if (NaN == NaN) {}
 if (NaN != NaN) {}
+
+// ...
+declare let x: any;
+if (NaN === x[0][1]) {}
 
 
 //// [nanEquality.js]
@@ -43,3 +47,4 @@ if (NaN === NaN) { }
 if (NaN !== NaN) { }
 if (NaN == NaN) { }
 if (NaN != NaN) { }
+if (NaN === x[0][1]) { }
diff --git a/tests/baselines/reference/nanEquality.symbols b/tests/baselines/reference/nanEquality.symbols
index e15fbcd7f3cfb..d5fe39946e14a 100644
--- a/tests/baselines/reference/nanEquality.symbols
+++ b/tests/baselines/reference/nanEquality.symbols
@@ -66,3 +66,11 @@ if (NaN != NaN) {}
 >NaN : Symbol(NaN, Decl(lib.es5.d.ts, --, --))
 >NaN : Symbol(NaN, Decl(lib.es5.d.ts, --, --))
 
+// ...
+declare let x: any;
+>x : Symbol(x, Decl(nanEquality.ts, 27, 11))
+
+if (NaN === x[0][1]) {}
+>NaN : Symbol(NaN, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(nanEquality.ts, 0, 13))
+
diff --git a/tests/baselines/reference/nanEquality.types b/tests/baselines/reference/nanEquality.types
index dc648ec437c65..e255f3e4144cb 100644
--- a/tests/baselines/reference/nanEquality.types
+++ b/tests/baselines/reference/nanEquality.types
@@ -90,3 +90,16 @@ if (NaN != NaN) {}
 >NaN : number
 >NaN : number
 
+// ...
+declare let x: any;
+>x : any
+
+if (NaN === x[0][1]) {}
+>NaN === x[0][1] : boolean
+>NaN : number
+>x[0][1] : any
+>x[0] : any
+>x : number
+>0 : 0
+>1 : 1
+
diff --git a/tests/cases/compiler/nanEquality.ts b/tests/cases/compiler/nanEquality.ts
index d8f66d61d9dda..23eff2ac4e057 100644
--- a/tests/cases/compiler/nanEquality.ts
+++ b/tests/cases/compiler/nanEquality.ts
@@ -23,3 +23,7 @@ if (NaN !== NaN) {}
 
 if (NaN == NaN) {}
 if (NaN != NaN) {}
+
+// ...
+declare let x: any;
+if (NaN === x[0][1]) {}
diff --git a/tests/cases/fourslash/fixNaNEquality1.ts b/tests/cases/fourslash/fixNaNEquality1.ts
index 1177793c9d307..52004b122fa2d 100644
--- a/tests/cases/fourslash/fixNaNEquality1.ts
+++ b/tests/cases/fourslash/fixNaNEquality1.ts
@@ -1,9 +1,10 @@
 /// <reference path="fourslash.ts" />
 
-////if (x === NaN) {}
+////declare const x: number;
+////[|if (x === NaN) {}|]
 
 verify.codeFix({
     index: 0,
     description: "Use `Number.isNaN(x)`.",
-    newFileContent: "if (Number.isNaN(x)) {}",
+    newRangeContent: "if (Number.isNaN(x)) {}",
 });
diff --git a/tests/cases/fourslash/fixNaNEquality2.ts b/tests/cases/fourslash/fixNaNEquality2.ts
index d93ada01867b3..e941ac7bd4f61 100644
--- a/tests/cases/fourslash/fixNaNEquality2.ts
+++ b/tests/cases/fourslash/fixNaNEquality2.ts
@@ -1,9 +1,10 @@
 /// <reference path="fourslash.ts" />
 
-////if (NaN === x) {}
+////declare const x: number;
+////[|if (NaN === x) {}|]
 
 verify.codeFix({
     index: 0,
     description: "Use `Number.isNaN(x)`.",
-    newFileContent: "if (Number.isNaN(x)) {}",
+    newRangeContent: "if (Number.isNaN(x)) {}",
 });
diff --git a/tests/cases/fourslash/fixNaNEquality3.ts b/tests/cases/fourslash/fixNaNEquality3.ts
index 434408b55dae6..6ae682a83c9a5 100644
--- a/tests/cases/fourslash/fixNaNEquality3.ts
+++ b/tests/cases/fourslash/fixNaNEquality3.ts
@@ -1,9 +1,10 @@
 /// <reference path="fourslash.ts" />
 
-////if (x !== NaN) {}
+////declare const x: number;
+////[|if (x !== NaN) {}|]
 
 verify.codeFix({
     index: 0,
     description: "Use `!Number.isNaN(x)`.",
-    newFileContent: "if (!Number.isNaN(x)) {}",
+    newRangeContent: "if (!Number.isNaN(x)) {}",
 });
diff --git a/tests/cases/fourslash/fixNaNEquality4.ts b/tests/cases/fourslash/fixNaNEquality4.ts
index 689305dbf640b..6f4128317b977 100644
--- a/tests/cases/fourslash/fixNaNEquality4.ts
+++ b/tests/cases/fourslash/fixNaNEquality4.ts
@@ -1,9 +1,10 @@
 /// <reference path="fourslash.ts" />
 
-////if (NaN !== x) {}
+////declare const x: number;
+////[|if (NaN !== x) {}|]
 
 verify.codeFix({
     index: 0,
     description: "Use `!Number.isNaN(x)`.",
-    newFileContent: "if (!Number.isNaN(x)) {}",
+    newRangeContent: "if (!Number.isNaN(x)) {}",
 });
diff --git a/tests/cases/fourslash/fixNaNEquality5.ts b/tests/cases/fourslash/fixNaNEquality5.ts
new file mode 100644
index 0000000000000..00b954f33bd59
--- /dev/null
+++ b/tests/cases/fourslash/fixNaNEquality5.ts
@@ -0,0 +1,10 @@
+/// <reference path="fourslash.ts" />
+
+////declare const x: any;
+////[|if (NaN !== x[0][1]) {}|]
+
+verify.codeFix({
+    index: 0,
+    description: "Use `!Number.isNaN(...)`.",
+    newRangeContent: "if (!Number.isNaN(x[0][1])) {}",
+});
diff --git a/tests/cases/fourslash/fixNaNEquality_all.ts b/tests/cases/fourslash/fixNaNEquality_all.ts
index c49a3ce20ebca..e5536ec8f041b 100644
--- a/tests/cases/fourslash/fixNaNEquality_all.ts
+++ b/tests/cases/fourslash/fixNaNEquality_all.ts
@@ -1,16 +1,22 @@
 /// <reference path="fourslash.ts" />
 
+////declare const x: number;
+////declare const y: any;
 ////if (x === NaN) {}
 ////if (NaN === x) {}
 ////if (x !== NaN) {}
 ////if (NaN !== x) {}
+////if (NaN === y[0][1]) {}
 
 verify.codeFixAll({
     fixId: "fixNaNEquality",
     fixAllDescription: ts.Diagnostics.Use_Number_isNaN_in_all_conditions.message,
     newFileContent:
-`if (Number.isNaN(x)) {}
+`declare const x: number;
+declare const y: any;
 if (Number.isNaN(x)) {}
+if (Number.isNaN(x)) {}
+if (!Number.isNaN(x)) {}
 if (!Number.isNaN(x)) {}
-if (!Number.isNaN(x)) {}`
+if (Number.isNaN(y[0][1])) {}`
 });