Coerce eq() argument all the time. Fixes #10616

src/core.js

@@ -264,9 +264,10 @@ jQuery.fn = jQuery.prototype = {
 	},
 
 	eq: function( i ) {
+		i = +i;
 		return i === -1 ?
 			this.slice( i ) :
-			this.slice( i, +i + 1 );
+			this.slice( i, i + 1 );
 	},
 
 	first: function() {

test/unit/traversing.js

@@ -630,3 +630,13 @@ test("add(String, Context)", function() {
 	deepEqual( jQuery( document.getElementById("firstp") ).add( "#ap", ctx ).get(), q( "firstp" ), "Add gEBId to selector, not in context" );
 	deepEqual( jQuery( document.getElementById("firstp") ).add( "#ap", document.getElementsByTagName("body")[0] ).get(), q( "firstp", "ap" ), "Add gEBId to selector, in context" );
 });
+
+test("eq('-1') #10616", function() {
+	expect(3);
+	var $divs = jQuery( "div" );
+
+	equal( $divs.eq( -1 ).length, 1, "The number -1 returns a selection that has length 1" );
+	equal( $divs.eq( "-1" ).length, 1, "The string '-1' returns a selection that has length 1" );
+	deepEqual( $divs.eq( "-1" ), $divs.eq( -1 ), "String and number -1 match" );
+});
+