diff --git a/src/random.h b/src/random.h
--- a/src/random.h
+++ b/src/random.h
@@ -173,6 +173,7 @@
 
     /** Generate a random integer in the range [0..range). */
     uint64_t randrange(uint64_t range) noexcept {
+        assert(range);
         --range;
         int bits = CountBits(range);
         while (true) {