diff --git a/src/triangulation.jl b/src/triangulation.jl
index a7335c2d..1dddc5c5 100644
--- a/src/triangulation.jl
+++ b/src/triangulation.jl
@@ -44,7 +44,7 @@ function triangulation_indices(p::Polyhedron)
     incident_idx = Dict(h => Set(incidentpointindices(p, h)) for h in h_idx)
     is_weak_adjacent = Dict((hi, hj) => !isempty(incident_idx[hi] ∩ incident_idx[hj]) for hi in h_idx for hj in h_idx)
     _triangulation(Δs, Δ, v_idx, h_idx, incident_idx, is_weak_adjacent, fulldim(p))
-    return Δs
+    return unique(Δs)
 end
 function triangulation(p::Polyhedron)
     return map(Δ -> vrep(get.(p, Δ)), triangulation_indices(p))
diff --git a/test/runtests.jl b/test/runtests.jl
index e164dcc7..0af2b70d 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -38,3 +38,4 @@ for (arith, T) in (("floating point", Float64), ("exact", Rational{BigInt}))
 end
 
 include("../examples/test_examples.jl")
+include("volume.jl")
diff --git a/test/volume.jl b/test/volume.jl
new file mode 100644
index 00000000..5dad3b50
--- /dev/null
+++ b/test/volume.jl
@@ -0,0 +1,147 @@
+using Test
+using Polyhedra
+using CDDLib
+
+# simple algorithm for calculating area of polygons
+# requires vertices to be sorted (counter)clockwise
+function shoelace(verts::AbstractMatrix{<:Real})
+    @assert size(verts, 1) == 2  "shoelace only works for polygons"
+    xs = verts[begin,:]
+    ys = verts[end,:]
+    A = (ys[end]+ys[begin])*(xs[end]-xs[begin])
+    for i in axes(verts,2)[begin:end-1]
+        A += (ys[i]+ys[i+1])*(xs[i]-xs[i+1])
+    end
+    A = abs(A)
+    A isa AbstractFloat ? A/2 : A//2
+end
+isvertsapprox = (verts, points) -> all(any(isapprox(p, v) for v in verts) for p in points)
+
+# issue 285: area of square [-0.5, -0.5] x [0.5, 0.5]
+
+ineq = [
+    HalfSpace([-2.0, -2.0], 4.0),
+    HalfSpace([-2.0, -1.0], 2.5),
+    HalfSpace([-2.0, 0.0], 2.0),
+    HalfSpace([-2.0, 1.0], 2.5),
+    HalfSpace([-2.0, 2.0], 4.0),
+    HalfSpace([-1.0, -2.0], 2.5),
+    HalfSpace([-1.0, -1.0], 1.0),
+    HalfSpace([-1.0, 0.0], 0.5),
+    HalfSpace([-1.0, 1.0], 1.0),
+    HalfSpace([-1.0, 2.0], 2.5),
+    HalfSpace([0.0, -2.0], 2.0),
+    HalfSpace([0.0, -1.0], 0.5),
+    HalfSpace([0.0, 0.0], 0.0),
+    HalfSpace([0.0, 1.0], 0.5),
+    HalfSpace([0.0, 2.0], 2.0),
+    HalfSpace([1.0, -2.0], 2.5),
+    HalfSpace([1.0, -1.0], 1.0),
+    HalfSpace([1.0, 0.0], 0.5),
+    HalfSpace([1.0, 1.0], 1.0),
+    HalfSpace([1.0, 2.0], 2.5),
+    HalfSpace([2.0, -2.0], 4.0),
+    HalfSpace([2.0, -1.0], 2.5),
+    HalfSpace([2.0, 0.0], 2.0),
+    HalfSpace([2.0, 1.0], 2.5),
+    HalfSpace([2.0, 2.0], 4.0),
+]
+square = polyhedron(reduce(intersect, ineq))
+sqverts = [-1 1 1 -1; -1 -1 1 1]/2
+@test isvertsapprox(eachcol(sqverts), points(square))
+@test volume(square) ≈ shoelace(sqverts)
+
+# issue 249
+
+poly = polyhedron(HalfSpace([-1.0, 0.0], 0.0) ∩
+                  HalfSpace([0.0, -1.0], 0.0) ∩
+                  HalfSpace([1.0, 0.0], 1.0) ∩
+                  HalfSpace([0.0, 1.0], 1.0) ∩
+                  HalfSpace([-0.2, -0.8], -0.0) ∩
+                  HalfSpace([0.6, 0.4], 0.6))
+
+verts = [1/3 1 0 0; 1 0 0 1]
+@test isvertsapprox(eachcol(verts), points(poly))
+@test volume(poly) ≈ shoelace(verts)
+
+poly2 = polyhedron(# HalfSpace([-1.0, 0.0], 0.0) ∩
+                    HalfSpace([0.0, -1.0], 0.0) ∩ # Comment here to get correct area
+                    HalfSpace([1.0, 0.0], 1.0) ∩
+                    HalfSpace([0.0, 1.0], 1.0) ∩
+                    HalfSpace([-0.6, -0.4], -0.6) ∩
+                    HalfSpace([0.2, 0.8], 0.95))
+verts2 = [1/3 3/4 1 1; 1 1 15/16 0]
+@test isvertsapprox(eachcol(verts2), points(poly2))
+@test volume(poly2) ≈ shoelace(verts2)
+
+lib=CDDLib.Library(:exact)
+L3 = polyhedron(vrep([
+    0 0 0 0 0 0
+    0 0 1 0 0 0
+    0 1 0 0 0 0
+    0 1 1 0 0 1
+    1 0 0 0 0 0
+    1 0 1 0 1 0
+    1 1 0 1 0 0
+    1 1 1 1 1 1
+    ]),lib)
+# reportedly solution taken from https://doi.org/10.1016/j.dam.2018.10.038
+@test volume(L3) == 1//180
+
+# examples similar to Cohen-Hickey paper, table 1
+# https://doi.org/10.1145/322139.322141
+s5 = polyhedron(vrep([
+    0 0 0 0 0
+    0 0 0 0 1
+    0 0 0 1 0
+    0 0 1 0 0
+    0 1 0 0 0
+    1 0 0 0 0
+    ]), lib)
+@test volume(s5) == 1//120
+
+flib = CDDLib.Library()
+
+ϕ = (1 + √5)/2
+isoc = polyhedron(vrep([
+     0  1  ϕ
+     0  1 -ϕ
+     0 -1  ϕ
+     0 -1 -ϕ
+     1  ϕ  0
+     1 -ϕ  0
+    -1  ϕ  0
+    -1 -ϕ  0
+     ϕ  0  1
+     ϕ  0 -1
+    -ϕ  0  1
+    -ϕ  0 -1
+    ]), flib)
+# https://en.wikipedia.org/wiki/Regular_icosahedron
+@test volume(isoc) ≈ (5/12)*(3+√5)*2^3
+
+ϕ² = ϕ^2
+dodec = polyhedron(vrep([
+     ϕ  ϕ  ϕ
+     ϕ  ϕ -ϕ
+     ϕ -ϕ  ϕ
+     ϕ -ϕ -ϕ
+    -ϕ  ϕ  ϕ
+    -ϕ  ϕ -ϕ
+    -ϕ -ϕ  ϕ
+    -ϕ -ϕ -ϕ
+     0  1  ϕ²
+     0  1 -ϕ²
+     0 -1  ϕ²
+     0 -1 -ϕ²
+     1  ϕ² 0
+     1 -ϕ² 0
+    -1  ϕ² 0
+    -1 -ϕ² 0
+     ϕ² 0  1
+     ϕ² 0 -1
+    -ϕ² 0  1
+    -ϕ² 0 -1
+    ]), flib)
+# https://en.wikipedia.org/wiki/Regular_dodecahedron
+@test volume(dodec) ≈ (1/4)*(15+7*√5)*2^3