diff --git a/src/propeller/downsample.cljc b/src/propeller/downsample.cljc
index 8037515..437ef3a 100644
--- a/src/propeller/downsample.cljc
+++ b/src/propeller/downsample.cljc
@@ -79,7 +79,7 @@
                                        (utils/filter-by-index distance-list (map #(:index %) tournament)))
                                      (map #(:distances %) new-downsample)))
             selected-case-index (metrics/argmax min-case-distances)]
-        (if (or (<= (apply max min-case-distances) case-delta) (zero? (count cases-to-pick-from)))
+        (if (or (= 0 (count tournament)) (<= (apply max min-case-distances) case-delta))
           new-downsample
           (do
             (if (sequential? (:input1 (first new-downsample)))
diff --git a/src/propeller/tools/metrics.cljc b/src/propeller/tools/metrics.cljc
index 2ead5ae..dfecf00 100755
--- a/src/propeller/tools/metrics.cljc
+++ b/src/propeller/tools/metrics.cljc
@@ -12,11 +12,13 @@
 (defn argmax
   "returns the index of the maximum value in a list, randomly tiebreaking"
   [coll]
-  (->> coll
-       (map-indexed vector)
-       (filter #(= (apply max coll) (second %)))
-       rand-nth
-       first))
+  (if (zero? (count coll))
+    :null
+    (->> coll
+         (map-indexed vector)
+         (filter #(= (apply max coll) (second %)))
+         rand-nth
+         first)))
 
 (defn mean
   "Returns the mean of a collection."