diff --git a/src/planar/macros.jl b/src/planar/macros.jl
index 1d76cc48..e10308d2 100644
--- a/src/planar/macros.jl
+++ b/src/planar/macros.jl
@@ -23,7 +23,7 @@ function planarparser(planarexpr, kwargs...)
 
     # braiding tensors need to be instantiated before kwargs are processed
     push!(parser.preprocessors, _construct_braidingtensors)
-    
+
     for (name, val) in kwargs
         if name == :order
             isexpr(val, :tuple) ||
@@ -62,7 +62,7 @@ function planarparser(planarexpr, kwargs...)
             throw(ArgumentError("Unknown keyword argument `name`."))
         end
     end
-    
+
     treebuilder = parser.contractiontreebuilder
     treesorter = parser.contractiontreesorter
     costcheck = parser.contractioncostcheck
diff --git a/src/planar/preprocessors.jl b/src/planar/preprocessors.jl
index 6c284ad9..2381c1f6 100644
--- a/src/planar/preprocessors.jl
+++ b/src/planar/preprocessors.jl
@@ -70,6 +70,7 @@ _add_adjoint(ex) = Expr(TO.prime, ex)
 
 # used by `@planar`: realize explicit braiding tensors
 function _construct_braidingtensors(ex::Expr)
+    # create a list of all tensors
     if TO.isdefinition(ex) || TO.isassignment(ex)
         lhs, rhs = TO.getlhs(ex), TO.getrhs(ex)
         if TO.istensorexpr(rhs)
@@ -89,11 +90,17 @@ function _construct_braidingtensors(ex::Expr)
         return Expr(ex.head, map(_construct_braidingtensors, ex.args)...)
     end
 
+    # create a mapping of tensor_expr => braiding_constructor_expr
     i = 1
     translatebraidings = Dict{Any,Any}()
     while i <= length(list)
         t = list[i]
         if _remove_adjoint(TO.gettensorobject(t)) == :τ
+            # verify that the braiding tensor has the correct form
+            obj, leftind, rightind = TO.decomposetensor(t)
+            length(leftind) == length(rightind) == 2 ||
+                throw(ArgumentError("Invalid expression $t. τ is reserved for the braiding, and should have two input and two output indices."))
+
             translatebraidings[t] = Expr(:call, GlobalRef(TensorKit, :BraidingTensor))
             deleteat!(list, i)
         else
@@ -101,93 +108,68 @@ function _construct_braidingtensors(ex::Expr)
         end
     end
 
-    unresolved = Any[] # list of indices that we couldn't yet figure out
-    indexmap = Dict{Any,Any}()
-    # indexmap[i] contains the expression to resolve the space for index i
-    for (t, construct_expr) in translatebraidings
-        obj, leftind, rightind = TO.decomposetensor(t)
-        length(leftind) == length(rightind) == 2 ||
-            throw(ArgumentError("The name τ is reserved for the braiding, and should have two input and two output indices."))
-        if _is_adjoint(obj)
-            i1b, i2b, = leftind
-            i2a, i1a, = rightind
-        else
-            i2b, i1b, = leftind
-            i1a, i2a, = rightind
-        end
-
-        obj_and_pos1a = _findindex(i1a, list)
-        obj_and_pos2a = _findindex(i2a, list)
-        obj_and_pos1b = _findindex(i1b, list)
-        obj_and_pos2b = _findindex(i2b, list)
-
-        if !isnothing(obj_and_pos1a)
-            indexmap[i1b] = Expr(:call, :space, obj_and_pos1a...)
-            indexmap[i1a] = Expr(:call, :space, obj_and_pos1a...)
-        elseif !isnothing(obj_and_pos1b)
-            indexmap[i1b] = Expr(TO.prime, Expr(:call, :space, obj_and_pos1b...))
-            indexmap[i1a] = Expr(TO.prime, Expr(:call, :space, obj_and_pos1b...))
-        else
-            push!(unresolved, (i1a, i1b))
-        end
+    # loop over the braiding tensors and try to figure out the correct spaces
+    ischanged = true
+    pre = Expr(:block)
+    while ischanged
+        ischanged = false
+        for (t, construct_expr) in translatebraidings
+            obj, leftind, rightind = TO.decomposetensor(t)
+            if _is_adjoint(obj)
+                i1b, i2b, = leftind
+                i2a, i1a, = rightind
+            else
+                i2b, i1b, = leftind
+                i1a, i2a, = rightind
+            end
 
-        if !isnothing(obj_and_pos2a)
-            indexmap[i2b] = Expr(:call, :space, obj_and_pos2a...)
-            indexmap[i2a] = Expr(:call, :space, obj_and_pos2a...)
-        elseif !isnothing(obj_and_pos2b)
-            indexmap[i2b] = Expr(TO.prime, Expr(:call, :space, obj_and_pos2b...))
-            indexmap[i2a] = Expr(TO.prime, Expr(:call, :space, obj_and_pos2b...))
-        else
-            push!(unresolved, (i2a, i2b))
-        end
-    end
-    # simple loop that tries to resolve as many indices as possible
-    changed = true
-    while changed == true
-        changed = false
-        i = 1
-        while i <= length(unresolved)
-            (i1, i2) = unresolved[i]
-            if i1 in keys(indexmap)
-                changed = true
-                indexmap[i2] = indexmap[i1]
-                deleteat!(unresolved, i)
-            elseif i2 in keys(indexmap)
-                changed = true
-                indexmap[i1] = indexmap[i2]
-                deleteat!(unresolved, i)
+            # attempt to deduce first space
+            obj_and_pos1a = _findindex(i1a, list)
+            obj_and_pos1b = _findindex(i1b, list)
+            if !isnothing(obj_and_pos1a)
+                V_i1b = Expr(:call, :space, obj_and_pos1a...)
+            elseif !isnothing(obj_and_pos1b)
+                V_i1b = Expr(TO.prime, Expr(:call, :space, obj_and_pos1b...))
             else
-                i += 1
+                continue
             end
-        end
-    end
-    !isempty(unresolved) &&
-        throw(ArgumentError("cannot determine the spaces of indices " *
-                            string(tuple(unresolved...)) *
-                            "for the braiding tensors in $(ex)"))
 
-    pre = Expr(:block)
-    for (t, construct_expr) in translatebraidings
-        obj, leftind, rightind = TO.decomposetensor(t)
-        if _is_adjoint(obj)
-            i1b, i2b, = leftind
-            i2a, i1a, = rightind
-        else
-            i2b, i1b, = leftind
-            i1a, i2a, = rightind
-        end
-        push!(construct_expr.args, indexmap[i1b])
-        push!(construct_expr.args, indexmap[i2b])
-        s = gensym(:τ)
-        push!(pre.args, :(@notensor $s = $construct_expr))
-        ex = TO.replacetensorobjects(ex) do o, l, r
-            if o == obj && l == leftind && r == rightind
-                return obj == :τ ? s : Expr(TO.prime, s)
+            # attempt to deduce second space
+            obj_and_pos2a = _findindex(i2a, list)
+            obj_and_pos2b = _findindex(i2b, list)
+            if !isnothing(obj_and_pos2a)
+                V_i2b = Expr(:call, :space, obj_and_pos2a...)
+            elseif !isnothing(obj_and_pos2b)
+                V_i2b = Expr(TO.prime, Expr(:call, :space, obj_and_pos2b...))
             else
-                return o
+                continue
+            end
+
+            # both spaces deduced, construct braidingtensor
+            push!(construct_expr.args, V_i1b)
+            push!(construct_expr.args, V_i2b)
+            s = gensym(:τ)
+            push!(pre.args, :(@notensor $s = $construct_expr))
+
+            # and insert into tensor expression and tensorlist
+            ex = TO.replacetensorobjects(ex) do o, l, r
+                if o == obj && l == leftind && r == rightind
+                    return obj == :τ ? s : Expr(TO.prime, s)
+                else
+                    return o
+                end
             end
+            push!(list,
+                  Expr(:typed_vcat, s, Expr(:tuple, leftind...),
+                       Expr(:tuple, rightind...)))
+
+            delete!(translatebraidings, t)
+            ischanged = true
         end
     end
+
+    @assert isempty(translatebraidings) "could not figure out all spaces \n $ex"
+
     return Expr(:block, pre, ex)
 end
 _construct_braidingtensors(x) = x
diff --git a/test/planar.jl b/test/planar.jl
index 062e41b6..755f6a46 100644
--- a/test/planar.jl
+++ b/test/planar.jl
@@ -71,29 +71,29 @@ end
 
 @testset "@planar" verbose = true begin
     T = ComplexF64
-    
+
     @testset "contractcheck" begin
         V = ℂ^2
         A = TensorMap(rand, T, V ⊗ V ← V)
         B = TensorMap(rand, T, V ⊗ V ← V')
         @tensor C1[i j; k l] := A[i j; m] * B[k l; m]
-        @tensor contractcheck=true C2[i j; k l] := A[i j; m] * B[k l; m]
+        @tensor contractcheck = true C2[i j; k l] := A[i j; m] * B[k l; m]
         @test C1 ≈ C2
         B2 = TensorMap(rand, T, V ⊗ V ← V) # wrong duality for third space
         @test_throws SpaceMismatch("incompatible spaces for m: $V ≠ $(V')") begin
             @tensor contractcheck = true C3[i j; k l] := A[i j; m] * B2[k l; m]
         end
-        
+
         A = TensorMap(rand, T, V ← V ⊗ V)
         B = TensorMap(rand, T, V ⊗ V ← V)
         @planar C1[i; j] := A[i; k l] * τ[k l; m n] * B[m n; j]
-        @planar contractcheck=true C2[i; j] := A[i; k l] * τ[k l; m n] * B[m n; j]
+        @planar contractcheck = true C2[i; j] := A[i; k l] * τ[k l; m n] * B[m n; j]
         @test C1 ≈ C2
         @test_throws SpaceMismatch("incompatible spaces for l: $V ≠ $(V')") begin
-            @planar contractcheck=true C3[i; j] := A[i; k l] * τ[k l; m n] * B[n j; m]
+            @planar contractcheck = true C3[i; j] := A[i; k l] * τ[k l; m n] * B[n j; m]
         end
     end
-    
+
     @testset "MPS networks" begin
         P = ℂ^2
         Vmps = ℂ^12
@@ -140,6 +140,23 @@ end
                                   conj(x′[1 3; -1])
         @test force_planar(ρ2) ≈ ρ2′
         @test ρ2 ≈ ρ3
+
+        # Periodic boundary conditions
+        # ----------------------------
+        f1 = isomorphism(storagetype(O), fuse(Vmpo^3), Vmpo ⊗ Vmpo' ⊗ Vmpo)
+        f2 = isomorphism(storagetype(O), fuse(Vmpo^3), Vmpo ⊗ Vmpo' ⊗ Vmpo)
+        f1′ = force_planar(f1)
+        f2′ = force_planar(f2)
+        @tensor O_periodic1[-1 -2; -3 -4] := O[1 -2; -3 2] * f1[-1; 1 3 4] *
+                                             conj(f2[-4; 2 3 4])
+        @plansor O_periodic2[-1 -2; -3 -4] := O[1 2; -3 6] * f1[-1; 1 3 5] *
+                                              conj(f2[-4; 6 7 8]) * τ[2 3; 7 4] *
+                                              τ[4 5; 8 -2]
+        @planar O_periodic′[-1 -2; -3 -4] := O′[1 2; -3 6] * f1′[-1; 1 3 5] *
+                                             conj(f2′[-4; 6 7 8]) * τ[2 3; 7 4] *
+                                             τ[4 5; 8 -2]
+        @test O_periodic1 ≈ O_periodic2
+        @test force_planar(O_periodic1) ≈ O_periodic′
     end
 
     @testset "MERA networks" begin
@@ -171,4 +188,22 @@ end
         end
         @test C ≈ C′
     end
+
+    @testset "Issue 93" begin
+        T = Float64
+        V1 = ℂ^2
+        V2 = ℂ^3
+        t1 = TensorMap(rand, T, V1 ← V2)
+        t2 = TensorMap(rand, T, V2 ← V1)
+
+        tr1 = @planar opt = true t1[a; b] * t2[b; a]
+        tr2 = @planar opt = true t1[d; a] * t2[b; c] * τ[c b; a d]
+        tr3 = @planar opt = true t1[d; a] * t2[b; c] * τ[a c; d b]
+        tr4 = @planar opt = true t1[f; a] * t2[c; d] * τ[d b; c e] * τ[e b; a f]
+        tr5 = @planar opt = true t1[f; a] * t2[c; d] * τ[d b; c e] * τ[a e; f b]
+        tr6 = @planar opt = true t1[f; a] * t2[c; d] * τ[c d; e b] * τ[e b; a f]
+        tr7 = @planar opt = true t1[f; a] * t2[c; d] * τ[c d; e b] * τ[a e; f b]
+
+        @test tr1 ≈ tr2 ≈ tr3 ≈ tr4 ≈ tr5 ≈ tr6 ≈ tr7
+    end
 end