diff --git a/src/PolynomialMatrixEquations.jl b/src/PolynomialMatrixEquations.jl
index 8bc1897cac839cc07c9d3c36660c7907d5248ce9..d2625ad9950f6374065c7ec13abb22dfb2e4064e 100644
--- a/src/PolynomialMatrixEquations.jl
+++ b/src/PolynomialMatrixEquations.jl
@@ -1,5 +1,9 @@
 module PolynomialMatrixEquations
 
+struct UnstableSystemException <: Exception end
+struct UndeterminateSystemException <: Exception end
+export UnstableSystemException, UndeterminateSystemException
+
 include("CyclicReduction.jl")
 export CyclicReductionWs, cyclic_reduction!, cyclic_reduction_check