diff --git a/Project.toml b/Project.toml
index 7c78b1a..56c7fb5 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "SBMLToolkit"
 uuid = "86080e66-c8ac-44c2-a1a0-9adaadfe4a4e"
 authors = ["paulflang", "anandijain"]
-version = "0.1.4"
+version = "0.1.5"
 
 [deps]
 Catalyst = "479239e8-5488-4da2-87a7-35f2df7eef83"
diff --git a/src/reactionsystem.jl b/src/reactionsystem.jl
index c61e242..a7d2760 100644
--- a/src/reactionsystem.jl
+++ b/src/reactionsystem.jl
@@ -22,6 +22,7 @@ function checksupport(filename::String)
     for item in not_implemented
         occursin(item, sbml) && throw(ErrorException("SBML models with $item are not yet implemented."))
     end
+    occursin("<sbml xmlns:fbc=", sbml) && throw(ErrorException("This model was designed for constrained-based optimisation. Please use COBREXA.jl instead of SBMLToolkit."))
 end
 
 """ Convert intensive to extensive mathematical expression """
@@ -167,7 +168,7 @@ function getunidirectionalcomponents(bidirectional_math)
     err = "Cannot separate bidirectional kineticLaw `$bidirectional_math` to forward and reverse part. Please make reaction irreversible or rearrange kineticLaw to the form `term1 - term2`."
     bidirectional_math = Symbolics.tosymbol(bidirectional_math)
     bidirectional_math = simplify(bidirectional_math; expand=true)
-    if (bidirectional_math isa Real) || (SymbolicUtils.operation(bidirectional_math) != +)
+    if (bidirectional_math isa Union{Real, Symbol}) || (SymbolicUtils.operation(bidirectional_math) != +)
         throw(ErrorException(err))
     end
     terms = SymbolicUtils.arguments(bidirectional_math)
diff --git a/test/reactionsystem.jl b/test/reactionsystem.jl
index 62b9506..ab0f47b 100644
--- a/test/reactionsystem.jl
+++ b/test/reactionsystem.jl
@@ -157,6 +157,7 @@ km = SBML.MathIdent("s1s2")
 sm1 = convert(Num, km)
 sm2 = sm - sm1
 @test_throws ErrorException SBMLToolkit.getunidirectionalcomponents(sm2)
+@test_throws ErrorException SBMLToolkit.getunidirectionalcomponents(:k1)
 
 # Test get_paramap
 trueparamap = [k1 => 1., c1 => 2.]