diff --git a/src/config-array.js b/src/config-array.js
index ccd8de4..4f3b7be 100644
--- a/src/config-array.js
+++ b/src/config-array.js
@@ -62,6 +62,19 @@ function assertValidFilesAndIgnores(config) {
 	FILES_AND_IGNORES_SCHEMA.validate(validateConfig);
 }
 
+/**
+ * A version of `path.relative()` that does not substitute `process.cwd()`
+ * when it sees an empty string. This is necessary because `basePath` can
+ * be an empty string in `ConfigArray`. In that case, we don't want the cwd
+ * to be substituted.
+ * @param {string} from The path to calculate from.
+ * @param {string} to The path to calculate to.
+ * @returns {string} The relative path between `from` and `to`.
+ */
+function safePathRelative(from, to) {
+	return from ? path.relative(from, to) : to;
+}
+
 /**
  * Wrapper around minimatch that caches minimatch patterns for
  * faster matching speed over multiple file path evaluations.
@@ -252,7 +265,7 @@ function pathMatchesIgnores(filePath, basePath, config) {
 	 * file path while strings are compared against the relative
 	 * file path.
 	 */
-	const relativeFilePath = path.relative(basePath, filePath);
+	const relativeFilePath = safePathRelative(basePath, filePath);
 
 	return Object.keys(config).length > 1 &&
 		!shouldIgnorePath(config.ignores, filePath, relativeFilePath);
@@ -277,7 +290,7 @@ function pathMatches(filePath, basePath, config) {
 	 * file path while strings are compared against the relative
 	 * file path.
 	 */
-	const relativeFilePath = path.relative(basePath, filePath);
+	const relativeFilePath = safePathRelative(basePath, filePath);
 
 	// match both strings and functions
 	const match = pattern => {
@@ -661,8 +674,10 @@ export class ConfigArray extends Array {
 			return result;
 		}
 
-		// TODO: Maybe move elsewhere? Maybe combine with getConfig() logic?
-		const relativeFilePath = path.relative(this.basePath, filePath);
+		/*
+		 * TODO: Maybe move elsewhere? Maybe combine with getConfig() logic?
+		 */
+		const relativeFilePath = safePathRelative(this.basePath, filePath);
 
 		if (shouldIgnorePath(this.ignores, filePath, relativeFilePath)) {
 			debug(`Ignoring ${filePath}`);
@@ -719,8 +734,10 @@ export class ConfigArray extends Array {
 			return finalConfig;
 		}
 
-		// TODO: Maybe move elsewhere?
-		const relativeFilePath = path.relative(this.basePath, filePath);
+		/*
+		 * TODO: Maybe move somewhere else?
+		 */
+		const relativeFilePath = safePathRelative(this.basePath, filePath);
 
 		if (shouldIgnorePath(this.ignores, filePath, relativeFilePath)) {
 			debug(`Ignoring ${filePath} based on file pattern`);
@@ -885,8 +902,7 @@ export class ConfigArray extends Array {
 
 		assertNormalized(this);
 
-		const relativeDirectoryPath = path.relative(this.basePath, directoryPath)
-			.replace(/\\/g, '/');
+		const relativeDirectoryPath = safePathRelative(this.basePath, directoryPath).replace(/\\/g, '/');
 
 		if (relativeDirectoryPath.startsWith('..')) {
 			return true;
diff --git a/tests/config-array.test.js b/tests/config-array.test.js
index 9cbcecb..92eaf5f 100644
--- a/tests/config-array.test.js
+++ b/tests/config-array.test.js
@@ -884,6 +884,93 @@ describe('ConfigArray', () => {
 
 			});	
 
+			// https://github.com/eslint/eslint/issues/17669
+			describe('basePath is an empty string', () => {
+
+				describe('with **/*.js', () => {					
+					beforeEach(() => {
+						configs = new ConfigArray([
+							{
+								files: ['**/*.js'],
+								defs: {
+									severity: 'error'
+								}
+							}
+						], { basePath: '', schema });
+		
+						configs.normalizeSync();
+					});
+	
+					it('should return a config when a filename matches a files pattern', () => {
+	
+						const config = configs.getConfig('foo.js');
+						expect(config).to.deep.equal({
+							defs: {
+								severity: 'error'
+							}
+						});
+					});
+	
+					it('should return a config when a relative path filename matches a files pattern', () => {
+	
+						const config = configs.getConfig('x/foo.js');
+						expect(config).to.deep.equal({
+							defs: {
+								severity: 'error'
+							}
+						});
+					});
+	
+					it('should return a config when an absolute path filename matches a files pattern', () => {
+	
+						const config = configs.getConfig('/x/foo.js');
+						expect(config).to.deep.equal({
+							defs: {
+								severity: 'error'
+							}
+						});
+					});
+				});
+
+				describe('with x/*.js', () => {					
+					beforeEach(() => {
+						configs = new ConfigArray([
+							{
+								files: ['x/*.js'],
+								defs: {
+									severity: 'error'
+								}
+							}
+						], { basePath: '', schema });
+		
+						configs.normalizeSync();
+					});
+	
+					it('should return undefined when a filename does not match a files pattern', () => {
+	
+						const config = configs.getConfig('foo.js');
+						expect(config).to.be.undefined;
+					});
+	
+					it('should return a config when a relative path filename matches a files pattern', () => {
+	
+						const config = configs.getConfig('x/foo.js');
+						expect(config).to.deep.equal({
+							defs: {
+								severity: 'error'
+							}
+						});
+					});
+	
+					it('should return undefined when an absolute path filename does not match a files pattern', () => {
+	
+						const config = configs.getConfig('/x/foo.js');
+						expect(config).to.be.undefined;
+					});
+				});
+
+			});
+
 		});
 
 		describe('isIgnored()', () => {
@@ -1742,6 +1829,69 @@ describe('ConfigArray', () => {
 				expect(configs.isExplicitMatch(filename)).to.be.false;
 			});
 
+			// https://github.com/eslint/eslint/issues/17669
+			describe('basePath is an empty string', () => {
+
+				describe('with **/*.js', () => {
+					
+					beforeEach(() => {
+						configs = new ConfigArray([
+							{
+								files: ['**/*.js'],
+								defs: {
+									severity: 'error'
+								}
+							}
+						], { basePath: '', schema });
+	
+						configs.normalizeSync();
+					});
+	
+					it('should return true when a filename matches a files pattern', () => {
+						expect(configs.isExplicitMatch('foo.js')).to.be.true;
+					});
+	
+					it('should return true when a relative path filename matches a files pattern', () => {
+						expect(configs.isExplicitMatch('x/foo.js')).to.be.true;
+					});
+	
+					it('should return true when an absolute path filename matches a files pattern', () => {
+						expect(configs.isExplicitMatch('/x/foo.js')).to.be.true;
+					});
+				});
+
+			});
+
+			describe('with x/*.js', () => {
+
+				beforeEach(() => {
+					configs = new ConfigArray([
+						{
+							files: ['x/*.js'],
+							defs: {
+								severity: 'error'
+							}
+						}
+					], { basePath: '', schema });
+
+					configs.normalizeSync();
+				});
+
+				it('should return false when a filename does not match a files pattern', () => {
+					expect(configs.isExplicitMatch('foo.js')).to.be.false;
+				});
+
+				it('should return true when a relative path filename matches a files pattern', () => {
+					expect(configs.isExplicitMatch('x/foo.js')).to.be.true;
+				});
+
+				it('should return false when an absolute path filename does not match a files pattern', () => {
+					expect(configs.isExplicitMatch('/x/foo.js')).to.be.false;
+				});
+				
+			});
+
+
 		});
 
 		describe('files', () => {