diff --git a/spec/util/IsNumeric-spec.ts b/spec/util/IsNumeric-spec.ts
new file mode 100644
index 0000000000..143df072d1
--- /dev/null
+++ b/spec/util/IsNumeric-spec.ts
@@ -0,0 +1,18 @@
+import {expect} from 'chai';
+import { isNumeric } from 'rxjs/util/isNumeric';
+
+/** @test {isNumeric} */
+describe('isNumeric', () => {
+   it('should cover the following numeric scenario', () => {
+     expect(isNumeric(' ')).to.be.false;
+     expect(isNumeric('\n')).to.be.false;
+     expect(isNumeric('\t')).to.be.false;
+
+     expect(isNumeric('0')).to.be.true;
+     expect(isNumeric(0)).to.be.true;
+     expect(isNumeric(-1)).to.be.true;
+     expect(isNumeric(-1.5)).to.be.true;
+     expect(isNumeric(6e6)).to.be.true;
+     expect(isNumeric('6e6')).to.be.true;
+  });
+});
diff --git a/src/internal/util/isNumeric.ts b/src/internal/util/isNumeric.ts
index 58eeb56e95..7983f471d3 100644
--- a/src/internal/util/isNumeric.ts
+++ b/src/internal/util/isNumeric.ts
@@ -1,6 +1,6 @@
 import { isArray } from './isArray';
 
-export function isNumeric(val: any): val is number {
+export function isNumeric(val: any): val is number | string {
   // parseFloat NaNs numeric-cast false positives (null|true|false|"")
   // ...but misinterprets leading-number strings, particularly hex literals ("0x...")
   // subtraction forces infinities to NaN