diff --git a/src/random.cpp b/src/random.cpp
index 092e04701..97e64bc8e 100644
--- a/src/random.cpp
+++ b/src/random.cpp
@@ -47,6 +47,7 @@ uint128_t GetRandUInt128(uint128_t nMax)
 
 int128_t GetRandInt128(int128_t nMax)
 {
+    assert(nMax >= 0);
     return GetRandUInt128(nMax);
 }
 
@@ -57,11 +58,13 @@ uint64_t GetRand(uint64_t nMax)
 
 int64_t GetRandInt64(int64_t nMax)
 {
+    assert(nMax >= 0);
     return GetRand(nMax);
 }
 
 int GetRandInt(int nMax)
 {
+    assert(nMax >= 0);
     return GetRand(nMax);
 }
 
diff --git a/src/random.h b/src/random.h
index 6a091ea3f..859c10715 100644
--- a/src/random.h
+++ b/src/random.h
@@ -24,7 +24,9 @@ void GetRandBytes(unsigned char* buf, size_t num);
 template <typename I>
 I GetRandGeneric(I nMax)
 {
+    // I must be an unsigned numeric type.
     static_assert(std::numeric_limits<I>::min() == 0);
+    // I() for primitive signed integer types returns 0.
     if (nMax == I())
         return I();
 
diff --git a/src/test/addrman_tests.cpp b/src/test/addrman_tests.cpp
index ae96d4f2e..0808fe406 100644
--- a/src/test/addrman_tests.cpp
+++ b/src/test/addrman_tests.cpp
@@ -31,6 +31,7 @@ public:
 
     int RandomInt(int nMax)
     {
+        assert(nMax >= 0);
         state = (CHashWriter(SER_GETHASH, 0) << state).GetHash().GetCheapHash();
         return (unsigned int)(state % nMax);
     }
diff --git a/src/weighted_map.h b/src/weighted_map.h
index 7511b9959..b641ec57d 100644
--- a/src/weighted_map.h
+++ b/src/weighted_map.h
@@ -22,13 +22,17 @@
 // weights of the children. This allows for addition, removal, and random
 // selection/dropping in logarithmic time.
 //
-// random(w) must be defined to return a uniform random value between zero
-// inclusive and w exclusive. The type W must support addition, binary and
-// unary -, and < comparisons, and W() must construct the zero value (these
-// constraints are met for primitive signed integer types).
+// random(w) (which will only be called with positive w) must be defined to
+// return a uniform random value between zero inclusive and w exclusive.
+// The type W must be a signed numeric type that supports addition, binary
+// and unary -, and < and <= comparisons, and W() must construct the zero value
+// (these constraints are met for primitive signed integer types).
 template <typename K, typename V, typename W, W random(W)>
 class WeightedMap
 {
+    // W must be a signed numeric type.
+    static_assert(std::numeric_limits<W>::min() < W());
+
     struct Node {
         K key;
         V value;
@@ -180,6 +184,7 @@ public:
             return std::nullopt;
         }
         W totalWeight = getTotalWeight();
+        assert(W() < totalWeight);
         W randomWeight = random(totalWeight);
         assert(W() <= randomWeight && randomWeight < totalWeight);
         size_t index = findByWeight(0, randomWeight);