diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 7f686076f1824..47223a350ef36 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1834,6 +1834,14 @@
         "category": "Error",
         "code": 1544
     },
+    "Confusing combination of '!' token and 'instanceof' keyword like 'a !instanceof b' is disallowed, as it might be misinterpreted as '!(a instanceof b)'": {
+        "category": "Error",
+        "code": 1545
+    },
+    "Confusing combination of '!' token and 'in' keyword like 'a !in b' is disallowed, as it might be misinterpreted as '!(a in b)'": {
+        "category": "Error",
+        "code": 1546
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",
diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index 50e827c17bd24..3098d84e22fd4 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -1967,7 +1967,18 @@ export function createScanner(
                         }
                         return pos += 2, token = SyntaxKind.ExclamationEqualsToken;
                     }
+                    const hasLeadingWhitespace = isWhiteSpaceLike(charCodeChecked(pos - 1));
                     pos++;
+                    const nextIdentifierToken = lookAhead(() => {
+                        tokenValue = scanIdentifierParts();
+                        return getIdentifierToken();
+                    });
+                    if (hasLeadingWhitespace && nextIdentifierToken === SyntaxKind.InKeyword) {
+                        error(Diagnostics.Confusing_combination_of_token_and_in_keyword_like_a_in_b_is_disallowed_as_it_might_be_misinterpreted_as_a_in_b);
+                    }
+                    if (hasLeadingWhitespace && nextIdentifierToken === SyntaxKind.InstanceOfKeyword) {
+                        error(Diagnostics.Confusing_combination_of_token_and_instanceof_keyword_like_a_instanceof_b_is_disallowed_as_it_might_be_misinterpreted_as_a_instanceof_b);
+                    }
                     return token = SyntaxKind.ExclamationToken;
                 case CharacterCodes.doubleQuote:
                 case CharacterCodes.singleQuote:
diff --git a/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.errors.txt b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.errors.txt
new file mode 100644
index 0000000000000..0cbd233deb38a
--- /dev/null
+++ b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.errors.txt
@@ -0,0 +1,32 @@
+confusingExclamationBeforeInAndInstanceOf.ts(8,4): error TS1545: Confusing combination of '!' token and 'instanceof' keyword like 'a !instanceof b' is disallowed, as it might be misinterpreted as '!(a instanceof b)'
+confusingExclamationBeforeInAndInstanceOf.ts(9,4): error TS1545: Confusing combination of '!' token and 'instanceof' keyword like 'a !instanceof b' is disallowed, as it might be misinterpreted as '!(a instanceof b)'
+confusingExclamationBeforeInAndInstanceOf.ts(15,4): error TS1546: Confusing combination of '!' token and 'in' keyword like 'a !in b' is disallowed, as it might be misinterpreted as '!(a in b)'
+confusingExclamationBeforeInAndInstanceOf.ts(16,4): error TS1546: Confusing combination of '!' token and 'in' keyword like 'a !in b' is disallowed, as it might be misinterpreted as '!(a in b)'
+
+
+==== confusingExclamationBeforeInAndInstanceOf.ts (4 errors) ====
+    declare let a: any;
+    declare let b: any;
+    
+    a! instanceof b; // should work
+    a!instanceof b; // should work
+    a/**/!instanceof b; // should work
+    a!/**/instanceof b; // should work
+    a !instanceof b; // should error
+       
+!!! error TS1545: Confusing combination of '!' token and 'instanceof' keyword like 'a !instanceof b' is disallowed, as it might be misinterpreted as '!(a instanceof b)'
+    a	!instanceof b; // should error
+     	 
+!!! error TS1545: Confusing combination of '!' token and 'instanceof' keyword like 'a !instanceof b' is disallowed, as it might be misinterpreted as '!(a instanceof b)'
+    
+    a! in b; // should work
+    a!in b; // should work
+    a/**/!in b; // should work
+    a!/**/in b; // should work
+    a !in b; // should error
+       
+!!! error TS1546: Confusing combination of '!' token and 'in' keyword like 'a !in b' is disallowed, as it might be misinterpreted as '!(a in b)'
+    a	!in b; // should error
+     	 
+!!! error TS1546: Confusing combination of '!' token and 'in' keyword like 'a !in b' is disallowed, as it might be misinterpreted as '!(a in b)'
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.js b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.js
new file mode 100644
index 0000000000000..c49a88e2e3493
--- /dev/null
+++ b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.js
@@ -0,0 +1,34 @@
+//// [tests/cases/compiler/confusingExclamationBeforeInAndInstanceOf.ts] ////
+
+//// [confusingExclamationBeforeInAndInstanceOf.ts]
+declare let a: any;
+declare let b: any;
+
+a! instanceof b; // should work
+a!instanceof b; // should work
+a/**/!instanceof b; // should work
+a!/**/instanceof b; // should work
+a !instanceof b; // should error
+a	!instanceof b; // should error
+
+a! in b; // should work
+a!in b; // should work
+a/**/!in b; // should work
+a!/**/in b; // should work
+a !in b; // should error
+a	!in b; // should error
+
+
+//// [confusingExclamationBeforeInAndInstanceOf.js]
+a instanceof b; // should work
+a instanceof b; // should work
+a /**/ instanceof b; // should work
+a /**/ instanceof b; // should work
+a instanceof b; // should error
+a instanceof b; // should error
+a in b; // should work
+a in b; // should work
+a /**/ in b; // should work
+a /**/ in b; // should work
+a in b; // should error
+a in b; // should error
diff --git a/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.symbols b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.symbols
new file mode 100644
index 0000000000000..4646982fb3f7a
--- /dev/null
+++ b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.symbols
@@ -0,0 +1,57 @@
+//// [tests/cases/compiler/confusingExclamationBeforeInAndInstanceOf.ts] ////
+
+=== confusingExclamationBeforeInAndInstanceOf.ts ===
+declare let a: any;
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+
+declare let b: any;
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a! instanceof b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a!instanceof b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a/**/!instanceof b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a!/**/instanceof b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a !instanceof b; // should error
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a	!instanceof b; // should error
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a! in b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a!in b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a/**/!in b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a!/**/in b; // should work
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a !in b; // should error
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
+a	!in b; // should error
+>a : Symbol(a, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 0, 11))
+>b : Symbol(b, Decl(confusingExclamationBeforeInAndInstanceOf.ts, 1, 11))
+
diff --git a/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.types b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.types
new file mode 100644
index 0000000000000..6165c34ddf9d8
--- /dev/null
+++ b/tests/baselines/reference/confusingExclamationBeforeInAndInstanceOf.types
@@ -0,0 +1,131 @@
+//// [tests/cases/compiler/confusingExclamationBeforeInAndInstanceOf.ts] ////
+
+=== confusingExclamationBeforeInAndInstanceOf.ts ===
+declare let a: any;
+>a : any
+>  : ^^^
+
+declare let b: any;
+>b : any
+>  : ^^^
+
+a! instanceof b; // should work
+>a! instanceof b : boolean
+>                : ^^^^^^^
+>a! : any
+>   : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a!instanceof b; // should work
+>a!instanceof b : boolean
+>               : ^^^^^^^
+>a! : any
+>   : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a/**/!instanceof b; // should work
+>a/**/!instanceof b : boolean
+>                   : ^^^^^^^
+>a/**/! : any
+>       : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a!/**/instanceof b; // should work
+>a!/**/instanceof b : boolean
+>                   : ^^^^^^^
+>a! : any
+>   : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a !instanceof b; // should error
+>a !instanceof b : boolean
+>                : ^^^^^^^
+>a ! : any
+>    : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a	!instanceof b; // should error
+>a	!instanceof b : boolean
+>                : ^^^^^^^
+>a	! : any
+>    : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a! in b; // should work
+>a! in b : boolean
+>        : ^^^^^^^
+>a! : any
+>   : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a!in b; // should work
+>a!in b : boolean
+>       : ^^^^^^^
+>a! : any
+>   : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a/**/!in b; // should work
+>a/**/!in b : boolean
+>           : ^^^^^^^
+>a/**/! : any
+>       : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a!/**/in b; // should work
+>a!/**/in b : boolean
+>           : ^^^^^^^
+>a! : any
+>   : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a !in b; // should error
+>a !in b : boolean
+>        : ^^^^^^^
+>a ! : any
+>    : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
+a	!in b; // should error
+>a	!in b : boolean
+>        : ^^^^^^^
+>a	! : any
+>    : ^^^
+>a : any
+>  : ^^^
+>b : any
+>  : ^^^
+
diff --git a/tests/cases/compiler/confusingExclamationBeforeInAndInstanceOf.ts b/tests/cases/compiler/confusingExclamationBeforeInAndInstanceOf.ts
new file mode 100644
index 0000000000000..66227cab625cd
--- /dev/null
+++ b/tests/cases/compiler/confusingExclamationBeforeInAndInstanceOf.ts
@@ -0,0 +1,16 @@
+declare let a: any;
+declare let b: any;
+
+a! instanceof b; // should work
+a!instanceof b; // should work
+a/**/!instanceof b; // should work
+a!/**/instanceof b; // should work
+a !instanceof b; // should error
+a	!instanceof b; // should error
+
+a! in b; // should work
+a!in b; // should work
+a/**/!in b; // should work
+a!/**/in b; // should work
+a !in b; // should error
+a	!in b; // should error