diff --git a/core/modules/widgets/widget.js b/core/modules/widgets/widget.js
index eb84fab4a..b73294654 100755
--- a/core/modules/widgets/widget.js
+++ b/core/modules/widgets/widget.js
@@ -335,7 +335,7 @@ Widget.prototype.makeFakeWidgetWithVariables = function(variables) {
 				};
 			} else {
 				opts = opts || {};
-				opts.variables = $tw.utils.extend(variables,opts.variables);
+				opts.variables = $tw.utils.extend({},variables,opts.variables);
 				return self.getVariableInfo(name,opts);
 			};
 		},
diff --git a/editions/test/tiddlers/tests/data/functions/FunctionFilterrunVariables4.tid b/editions/test/tiddlers/tests/data/functions/FunctionFilterrunVariables4.tid
new file mode 100644
index 000000000..d78b211ad
--- /dev/null
+++ b/editions/test/tiddlers/tests/data/functions/FunctionFilterrunVariables4.tid
@@ -0,0 +1,20 @@
+title: Functions/FunctionFilterrunVariables4
+description: Nested functions in filter runs that set variables should not pollute upstream widget tree
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\function .a() [.b[]]
+\function .b() [all[]] :map[subtract[1].c[]]
+\function .c() [all[]] :map[subtract[1].d[]]
+\function .d() [all[]] :map[subtract[1].e[]]
+\function .e() [all[]] :map[subtract[1]]
+
+
+<$text text={{{ [[10]] :map:flat[.a[]then<currentTiddler>] }}}/>
+
++
+title: ExpectedResult
+
+10
\ No newline at end of file