diff --git a/Project.toml b/Project.toml
index eed1423..001c27c 100644
--- a/Project.toml
+++ b/Project.toml
@@ -2,7 +2,7 @@ name = "PhyloCoalSimulations"
 uuid = "53f7b83a-06b5-4910-9a21-1896bf762ade"
 authors = ["Cecile Ane <cecileane@users.noreply.github.com>",
            "John Fogg <70609062+fogg-uw@users.noreply.github.com>"]
-version = "0.1.0"
+version = "0.1.1"
 
 [deps]
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"
diff --git a/src/simulatecoalescent_network.jl b/src/simulatecoalescent_network.jl
index 8fbbf7e..b5df6a3 100644
--- a/src/simulatecoalescent_network.jl
+++ b/src/simulatecoalescent_network.jl
@@ -158,6 +158,7 @@ function simulatecoalescent(net::PN.HybridNetwork, nloci::Integer, nindividuals;
     inheritancecorrelation <= 1.0 || error("the inheritance correlation should be <= 1")
     independentlin = (inheritancecorrelation == 0.0)
     alpha = (1-inheritancecorrelation)/inheritancecorrelation # correlation = 1/(1+alpha)
+    PN.check_nonmissing_nonnegative_edgelengths(net, "the coalescent process cannot be simulated")
     for e in net.edge
         e.hybrid && e.gamma == -1.0 && error("the network needs gamma values")
     end
@@ -334,6 +335,7 @@ function simulatecoalescent(net::PN.HybridNetwork, nloci::Integer, nindividuals,
         error("populationsize should be a number or dictionary")
     end
     # network with lengths in coalescent units
+    PN.check_nonmissing_nonnegative_edgelengths(net, "the coalescent process cannot be simulated")
     net_coal = deepcopy(net)
     for e in net_coal.edge
         e.length = e.length / Neff[e.number]