diff --git a/core/matching/query_matching.go b/core/matching/query_matching.go
index 731a30625..8b890af06 100644
--- a/core/matching/query_matching.go
+++ b/core/matching/query_matching.go
@@ -31,14 +31,15 @@ func QueryMatching(requestMatcher models.RequestMatcher, toMatch map[string][]st
 		}
 	}
 
+	lowercaseKeyMap := make(map[string][]string)
 	for key, value := range toMatch {
-		toMatch[strings.ToLower(key)] = value
+		lowercaseKeyMap[strings.ToLower(key)] = value
 	}
 
 	for matcherQueryKey, matcherQueryValue := range *requestMatcher.Query {
 		matcherHeaderValueMatched := false
 
-		toMatchQueryValues, found := toMatch[strings.ToLower(matcherQueryKey)]
+		toMatchQueryValues, found := lowercaseKeyMap[strings.ToLower(matcherQueryKey)]
 		if !found {
 			matched = false
 			continue
diff --git a/core/matching/query_matching_test.go b/core/matching/query_matching_test.go
index b56e39d14..c44448cc4 100644
--- a/core/matching/query_matching_test.go
+++ b/core/matching/query_matching_test.go
@@ -182,3 +182,26 @@ func Test_QueryMatching(t *testing.T) {
 	}
 
 }
+
+func Test_QueryMatching_ShouldNotModifySourceQueries(t *testing.T) {
+	RegisterTestingT(t)
+
+	toMatch := map[string][]string{
+		"urlPattern": {"test-(.+).com"},
+	}
+
+	result := matching.QueryMatching(models.RequestMatcher{
+		Query: &models.QueryRequestFieldMatchers{
+			"urlPattern": {
+				{
+					Matcher: matchers.Glob,
+					Value:   "test-(.+).com",
+				},
+			},
+		},
+	}, toMatch)
+
+	Expect(result.Matched).To(BeTrue())
+	Expect(len(toMatch)).To(Equal(1))
+	Expect(toMatch["urlPattern"]).To(Equal([]string{"test-(.+).com"}))
+}