diff --git a/src/Factor.jl b/src/Factor.jl
index 241b648ec4..7d7ec7be74 100644
--- a/src/Factor.jl
+++ b/src/Factor.jl
@@ -56,6 +56,10 @@ _is_legal(a::Fac) = xor(isdefined(a, :fac), isdefined(a, :arr))
 
 _is_dic(a::Fac) = _is_legal(a) && isdefined(a, :fac)
 
+function Base.:(==)(F1::Fac, F2::Fac)
+  error("Equality testing of factorizations is not supported")
+end
+
 @doc raw"""
     unit(a::Fac{T}) -> T
 
diff --git a/test/Factor-test.jl b/test/Factor-test.jl
index a2582744b5..d154dbffcd 100644
--- a/test/Factor-test.jl
+++ b/test/Factor-test.jl
@@ -29,3 +29,12 @@ end
    @test string(f) == "x * (x + y) * (x*y)" ||
          string(f) == "x * (x*y) * (x + y)"
 end
+
+@testset "Fac.equality" begin
+  # 2025-10-20  equality test on factorizations always gives error (even if the args are ===)
+   f = Fac(-1, Dict{Int, Int}(2 => 3, 3 => 1))
+   ff = Fac(-1, [2 => 3, 3 => 1])
+
+   @test_throws  ErrorException  f == f
+   @test_throws  ErrorException  (f == ff) 
+end