diff --git a/src/ziggurat/metrics.clj b/src/ziggurat/metrics.clj
index 6f3f161d..56ef1a0f 100644
--- a/src/ziggurat/metrics.clj
+++ b/src/ziggurat/metrics.clj
@@ -14,8 +14,11 @@
 (defn- merge-tags
   [additional-tags]
   (let [default-tags {"actor" (:app-name (ziggurat-config))}]
-    (merge default-tags (when-not (seq additional-tags)
-                          (stringify-keys additional-tags)))))
+    (merge default-tags (stringify-keys additional-tags))))
+
+(defn- get-tagged-metric
+  [metric-name tags]
+  (.tagged ^MetricName metric-name tags))
 
 (defn mk-meter
   ([category metric]
@@ -24,7 +27,7 @@
    (let [namespace     (str category "." metric)
          metric-name   (MetricRegistry/name ^String namespace nil)
          tags          (merge-tags additional-tags)
-         tagged-metric (.tagged ^MetricName metric-name tags)]
+         tagged-metric (get-tagged-metric metric-name tags)]
      (.meter ^MetricRegistry metrics-registry ^MetricName tagged-metric))))
 
 (defn mk-histogram
diff --git a/test/ziggurat/metrics_test.clj b/test/ziggurat/metrics_test.clj
index 8ae9c3ac..32db653a 100644
--- a/test/ziggurat/metrics_test.clj
+++ b/test/ziggurat/metrics_test.clj
@@ -1,21 +1,48 @@
 (ns ziggurat.metrics-test
   (:require [clojure.test :refer :all]
+            [clojure.walk :refer [stringify-keys]]
+            [ziggurat.config :refer [ziggurat-config]]
+            [ziggurat.fixtures :as fix]
             [ziggurat.metrics :as metrics])
   (:import (io.dropwizard.metrics5 Meter Histogram UniformReservoir)))
 
+(use-fixtures :once fix/mount-only-config)
+
 (deftest mk-meter-test
-  (testing "returns a meter"
-    (let [category "category"
-          metric   "metric1"
-          meter    (metrics/mk-meter category metric)]
-      (is (instance? Meter meter)))))
+  (let [category     "category"
+        metric       "metric1"
+        service-name (:app-name (ziggurat-config))]
+    (testing "returns a meter"
+      (let [expected-tags {"actor" service-name}]
+        (with-redefs [metrics/get-tagged-metric (fn [metric-name tags]
+                                                  (is (= tags expected-tags))
+                                                  (.tagged metric-name tags))]
+          (is (instance? Meter (metrics/mk-meter category metric))))))
+    (testing "returns a meter - with additional-tags"
+      (let [additional-tags {:foo "bar"}
+            expected-tags   (merge {"actor" service-name} (stringify-keys additional-tags))]
+        (with-redefs [metrics/get-tagged-metric (fn [metric-name tags]
+                                                  (is (= tags expected-tags))
+                                                  (.tagged metric-name tags))]
+          (is (instance? Meter (metrics/mk-meter category metric additional-tags))))))))
 
 (deftest mk-histogram-test
-  (testing "returns a histogram"
-    (let [category "category"
-          metric   "metric2"
-          meter    (metrics/mk-histogram category metric)]
-      (is (instance? Histogram meter)))))
+  (let [category     "category"
+        metric       "metric2"
+        service-name (:app-name (ziggurat-config))]
+    (testing "returns a histogram"
+      (let [expected-tags {"actor" service-name}]
+        (with-redefs [metrics/get-tagged-metric (fn [metric-name tags]
+                                                  (is (= tags expected-tags))
+                                                  (.tagged metric-name tags))]
+          (is (instance? Histogram (metrics/mk-histogram category metric))))))
+    (testing "returns a histogram - with additional-tags"
+      (let [additional-tags {:foo "bar"}
+            expected-tags   (merge {"actor" service-name} (stringify-keys additional-tags))]
+        (with-redefs [metrics/get-tagged-metric (fn [metric-name tags]
+                                                  (is (= tags expected-tags))
+                                                  (.tagged metric-name tags))]
+          (is (instance? Histogram (metrics/mk-histogram category metric additional-tags))))))))
 
 (deftest increment-count-test
   (let [metric                     "metric3"