diff --git a/core/modules/widgets/importvariables.js b/core/modules/widgets/importvariables.js
index e720dc07b..3ea1d1174 100644
--- a/core/modules/widgets/importvariables.js
+++ b/core/modules/widgets/importvariables.js
@@ -61,7 +61,14 @@ ImportVariablesWidget.prototype.execute = function(tiddlerList) {
 					var widget = widgetPointer.makeChildWidget(node);
 					widget.computeAttributes();
 					widget.execute();
-					$tw.utils.extend(widgetPointer.variables,widget.variables);
+					// We SHALLOW copy over all variables
+					// in widget. We can't use
+					// $tw.utils.assign, because that copies
+					// up the prototype chain, which we
+					// don't want.
+					$tw.utils.each(Object.keys(widget.variables), function(key) {
+						widgetPointer.variables[key] = widget.variables[key];
+					});
 				} else {
 					widgetPointer.makeChildWidgets([node]);
 					widgetPointer = widgetPointer.children[0];
diff --git a/editions/test/tiddlers/tests/test-widget.js b/editions/test/tiddlers/tests/test-widget.js
index 5983b97dd..c20305746 100755
--- a/editions/test/tiddlers/tests/test-widget.js
+++ b/editions/test/tiddlers/tests/test-widget.js
@@ -517,6 +517,38 @@ describe("Widget module", function() {
 		// Test the rendering
 		expect(wrapper.innerHTML).toBe("<p>Don't forget me.</p>");
 	});
+
+	/** This test reproduces issue #4504.
+	 *
+	 * The importvariable widget was creating redundant copies into
+	 * itself of variables in widgets higher up in the tree. Normally,
+	 * this caused no errors, but it would mess up qualify-macros.
+	 * They would find multiple instances of the same transclusion
+	 * variable if a transclusion occured higher up in the widget tree
+	 * than an importvariables AND that importvariables was importing
+	 * at least ONE variable.
+	 */
+	it("adding imported variables doesn't change qualifyers", function() {
+		var wiki = new $tw.Wiki();
+		function wikiparse(text) {
+			var tree = parseText(text,wiki);
+			var widgetNode = createWidgetNode(tree,wiki);
+			var wrapper = renderWidgetNode(widgetNode);
+			return wrapper.innerHTML;
+		};
+		wiki.addTiddlers([
+			{title: "body", text: "\\import A\n<<qualify this>>"},
+			{title: "A", text: "\\define unused() ignored"}
+		]);
+		// This transclude wraps "body", which has an
+		// importvariable widget in it.
+		var withA = wikiparse("{{body}}");
+		wiki.addTiddler({title: "A", text: ""});
+		var withoutA = wikiparse("{{body}}");
+		// Importing two different version of "A" shouldn't cause
+		// the <<qualify>> widget to spit out something different.
+		expect(withA).toBe(withoutA);
+	});
 });
 
 })();