diff --git a/test/test_ddp.jl b/test/test_ddp.jl
index c9bbb867..36568174 100644
--- a/test/test_ddp.jl
+++ b/test/test_ddp.jl
@@ -431,6 +431,23 @@ Tests for markov/ddp.jl
                 @test Matrix(_ddp.Q) == _Q
             end
         end
+
+        # the unsorted inputs must not be mutated by construction, and
+        # constructing from the same arrays again must succeed (issue
+        # #117); fresh inputs per Q format, never passed to a constructor
+        # before, so that the literal baselines cannot be contaminated
+        for make_Q in (identity, sparse)
+            s_in, a_in = [1, 2, 1], [1, 1, 2]
+            R_in = [0.0, 2.0, 1.0]
+            Q_in = make_Q([1.0 0.0; 0.0 1.0; 0.5 0.5])
+            for _ in 1:2  # reconstruction from the same arrays must succeed
+                _ddp = DiscreteDP(R_in, Q_in, beta, s_in, a_in)
+                @test s_in == [1, 2, 1]
+                @test a_in == [1, 1, 2]
+                @test R_in == [0.0, 2.0, 1.0]
+                @test Matrix(Q_in) == [1.0 0.0; 0.0 1.0; 0.5 0.5]
+            end
+        end
     end
 
     @testset "num_sa_pairs and form converters" begin