diff --git a/src/vs/platform/contextkey/common/contextkey.ts b/src/vs/platform/contextkey/common/contextkey.ts
index d360fda192a00..b59849d296bb9 100644
--- a/src/vs/platform/contextkey/common/contextkey.ts
+++ b/src/vs/platform/contextkey/common/contextkey.ts
@@ -128,8 +128,6 @@ const defaultConfig: ParserConfig = {
 	regexParsingWithErrorRecovery: true
 };
 
-class ParseError extends Error { }
-
 export type ParsingError = {
 	message: string;
 	offset: number;
@@ -167,6 +165,8 @@ export class Parser {
 	// Note: this doesn't produce an exact syntax tree but a normalized one
 	// ContextKeyExpression's that we use as AST nodes do not expose constructors that do not normalize
 
+	private static _parseError = new Error();
+
 	// lifetime note: `_scanner` lives as long as the parser does, i.e., is not reset between calls to `parse`
 	private readonly _scanner = new Scanner();
 
@@ -211,11 +211,11 @@ export class Parser {
 				const peek = this._peek();
 				const additionalInfo = peek.type === TokenType.Str ? hintUnexpectedToken : undefined;
 				this._parsingErrors.push({ message: errorUnexpectedToken, offset: peek.offset, lexeme: Scanner.getLexeme(peek), additionalInfo });
-				throw new ParseError();
+				throw Parser._parseError;
 			}
 			return expr;
 		} catch (e) {
-			if (!(e instanceof ParseError)) {
+			if (!(e === Parser._parseError)) {
 				throw e;
 			}
 			return undefined;
@@ -311,7 +311,7 @@ export class Parser {
 						}
 						const regexLexeme = expr.lexeme;
 						const closingSlashIndex = regexLexeme.lastIndexOf('/');
-						const flags = closingSlashIndex === regexLexeme.length - 1 ? undefined : regexLexeme.substring(closingSlashIndex + 1);
+						const flags = closingSlashIndex === regexLexeme.length - 1 ? undefined : this._removeFlagsGY(regexLexeme.substring(closingSlashIndex + 1));
 						let regexp: RegExp | null;
 						try {
 							regexp = new RegExp(regexLexeme.substring(1, closingSlashIndex), flags);
@@ -365,7 +365,7 @@ export class Parser {
 
 							const regexLexeme = lexemeReconstruction.join('');
 							const closingSlashIndex = regexLexeme.lastIndexOf('/');
-							const flags = closingSlashIndex === regexLexeme.length - 1 ? undefined : regexLexeme.substring(closingSlashIndex + 1);
+							const flags = closingSlashIndex === regexLexeme.length - 1 ? undefined : this._removeFlagsGY(regexLexeme.substring(closingSlashIndex + 1));
 							let regexp: RegExp | null;
 							try {
 								regexp = new RegExp(regexLexeme.substring(1, closingSlashIndex), flags);
@@ -481,7 +481,7 @@ export class Parser {
 
 			case TokenType.EOF:
 				this._parsingErrors.push({ message: errorUnexpectedEOF, offset: peek.offset, lexeme: '', additionalInfo: hintUnexpectedEOF });
-				throw new ParseError();
+				throw Parser._parseError;
 
 			default:
 				throw this._errExpectedButGot(`true | false | KEY \n\t| KEY '=~' REGEX \n\t| KEY ('==' | '!=' | '<' | '<=' | '>' | '>=' | 'in' | 'not' 'in') value`, this._peek());
@@ -512,6 +512,11 @@ export class Parser {
 		}
 	}
 
+	private _flagsGYRe = /g|y/g;
+	private _removeFlagsGY(flags: string): string {
+		return flags.replaceAll(this._flagsGYRe, '');
+	}
+
 	// careful: this can throw if current token is the initial one (ie index = 0)
 	private _previous() {
 		return this._tokens[this._current - 1];
@@ -546,7 +551,7 @@ export class Parser {
 		const offset = got.offset;
 		const lexeme = Scanner.getLexeme(got);
 		this._parsingErrors.push({ message, offset, lexeme, additionalInfo });
-		return new ParseError();
+		return Parser._parseError;
 	}
 
 	private _check(type: TokenType) {
@@ -1558,7 +1563,7 @@ function eliminateConstantsInArray(arr: ContextKeyExpression[]): (ContextKeyExpr
 	return newArr;
 }
 
-class ContextKeyAndExpr implements IContextKeyExpression {
+export class ContextKeyAndExpr implements IContextKeyExpression {
 
 	public static create(_expr: ReadonlyArray<ContextKeyExpression | null | undefined>, negated: ContextKeyExpression | null, extraRedundantCheck: boolean): ContextKeyExpression | undefined {
 		return ContextKeyAndExpr._normalizeArr(_expr, negated, extraRedundantCheck);
@@ -1757,7 +1762,7 @@ class ContextKeyAndExpr implements IContextKeyExpression {
 	}
 }
 
-class ContextKeyOrExpr implements IContextKeyExpression {
+export class ContextKeyOrExpr implements IContextKeyExpression {
 
 	public static create(_expr: ReadonlyArray<ContextKeyExpression | null | undefined>, negated: ContextKeyExpression | null, extraRedundantCheck: boolean): ContextKeyExpression | undefined {
 		return ContextKeyOrExpr._normalizeArr(_expr, negated, extraRedundantCheck);
diff --git a/src/vs/platform/contextkey/test/common/parser.test.ts b/src/vs/platform/contextkey/test/common/parser.test.ts
index 0c462e54d84d9..6d08961dae8c9 100644
--- a/src/vs/platform/contextkey/test/common/parser.test.ts
+++ b/src/vs/platform/contextkey/test/common/parser.test.ts
@@ -176,9 +176,9 @@ suite('Context Key Parser', () => {
 			assert.deepStrictEqual(parseToStr(input), "resource =~ /((\\/scratch\\/(?!update)(.*)\\/)|((\\/src\\/).*\\/)).*$/");
 		});
 
-		test(`resourcePath =~ /\.md(\.yml|\.txt)*$/gim`, () => {
-			const input = `resourcePath =~ /\.md(\.yml|\.txt)*$/gim`;
-			assert.deepStrictEqual(parseToStr(input), "resourcePath =~ /.md(.yml|.txt)*$/gim");
+		test(`resourcePath =~ /\.md(\.yml|\.txt)*$/giym`, () => {
+			const input = `resourcePath =~ /\.md(\.yml|\.txt)*$/giym`;
+			assert.deepStrictEqual(parseToStr(input), "resourcePath =~ /.md(.yml|.txt)*$/im");
 		});
 
 	});