diff --git a/src/Tools/Random.cc b/src/Tools/Random.cc
--- a/src/Tools/Random.cc
+++ b/src/Tools/Random.cc
@@ -1,58 +1,58 @@
 // -*- C++ -*-
 #include "Rivet/Config/RivetCommon.hh"
 #include <random>
 #if defined(_OPENMP)
 #include "omp.h"
 #endif
 
 namespace Rivet {
 
 
   // Return a thread-safe random number generator
   std::mt19937& rng() {
     #if defined(_OPENMP)
     static map<int,std::mt19937> gens;
     const int nthread = omp_get_thread_num();
     if (gens.find(nthread) == gens.end()) {
       // Make seeds for each thread, either via the standard seed generator or based on a fixed seed from the environment
       vector<uint32_t> seeds(nthread+1);
-      const uint32_t envseed = getEnvParam<uint32_t>("RIVET_RANDOM_SEED", -1);
+      const uint32_t envseed = getEnvParam<uint32_t>("RIVET_RANDOM_SEED", 0);
       if (envseed > 0) {
         std::iota(seeds.begin(), seeds.end(), envseed);
       } else {
         std::seed_seq seq{1,2,3,4,5};
         seq.generate(seeds.begin(), seeds.end());
       }
       gens[nthread] = std::mt19937(seeds[nthread]);
       // cout << "Thread " << nthread+1 << ", seed=" << seeds[nthread] << " (" << gens.size() << " RNGs)" << '\n';
     }
     std::mt19937& g = gens[nthread];
     #else
     static std::mt19937 g(12345);
     #endif
     return g;
   }
 
 
   // Return a uniformly sampled random number between 0 and 1
   double rand01() {
     // return rand() / (double)RAND_MAX;
     return std::generate_canonical<double, 32>(rng()); ///< @todo What's the "correct" number of bits of randomness?
   }
 
 
   // Return a Gaussian/normal sampled random number with the given mean and width
   double randnorm(double loc, double scale) {
     std::normal_distribution<> d(loc, scale);
     return d(rng());
   }
 
 
   // Return a log-normal sampled random number
   double randlognorm(double loc, double scale) {
     std::lognormal_distribution<> d(loc, scale);
     return d(rng());
   }
 
 
 }