diff --git a/CHANGES.md b/CHANGES.md
index 3b74903c..6414b218 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,6 +2,8 @@
 
 Changes since v2.1.0 include:
 
+- Fix crash on summary output when numpy is not installed.
+
 # Flent v2.1.0 #
 Released on 2022-11-02.
 
diff --git a/flent/combiners.py b/flent/combiners.py
index ca133ce8..90e17462 100644
--- a/flent/combiners.py
+++ b/flent/combiners.py
@@ -606,6 +606,9 @@ class Pct99Reducer(TryReducer):
     raw_key = "pct99"
 
     def _reduce(self, data):
+        if not HAS_NUMPY:
+            return sorted(data)[-(len(data) // 100 + 1)]
+
         return np.percentile(data, 99)
 
 class CumsumReducer(TryReducer):
@@ -740,6 +743,9 @@ def _reduce(self, data):
 class RawPct99Reducer(RawReducer):
 
     def _reduce(self, data):
+        if not HAS_NUMPY:
+            return sorted(data)[-(len(data) // 100 + 1)]
+
         return np.percentile(data, 99)
 
 class RawCumsumReducer(RawReducer):