diff --git a/src/QuantumClifford.jl b/src/QuantumClifford.jl
index e7f083981..f1b3b6aa6 100644
--- a/src/QuantumClifford.jl
+++ b/src/QuantumClifford.jl
@@ -993,10 +993,14 @@ end
 # Conversion and promotion
 ##############################
 
-Base.promote_rule(::Type{<:Stabilizer{T}}       ,  ::Type{<:Destabilizer{T}}   ) where {T<:Tableau} = MixedDestabilizer{T}
-Base.promote_rule(::Type{<:MixedDestabilizer{T}},  ::Type{<:Stabilizer{T}}     ) where {T<:Tableau} = MixedDestabilizer{T}
-
-Base.convert(::Type{<:MixedDestabilizer{T}}, x::Union{Destabilizer{T}, Stabilizer{T}}) where {T <: Tableau} = MixedDestabilizer(x)
+# Destabilizer, MixedDestabilizer -> MixedDestabilizer
+Base.promote_rule(::Type{<:Destabilizer{T}}   , ::Type{<:MixedDestabilizer{T}}) where {T<:Tableau} = MixedDestabilizer{T}
+# MixedStabilizer, MixedDestabilizer -> MixedDestabilizer
+Base.promote_rule(::Type{<:MixedStabilizer{T}}, ::Type{<:MixedDestabilizer{T}}) where {T<:Tableau} = MixedDestabilizer{T}
+# Stabilizer, T<:Union{MixedStabilizer, Destabilizer, MixedDestabilizer} -> T
+Base.promote_rule(::Type{<:Stabilizer{T}}     , ::Type{<:S}                   ) where {T<:Tableau, S<:Union{MixedStabilizer{T}, Destabilizer{T}, MixedDestabilizer{T}}} = S
+
+Base.convert(::Type{<:MixedDestabilizer{T}}, x::Union{Destabilizer{T}, MixedStabilizer{T}, Stabilizer{T}}) where {T <: Tableau} = MixedDestabilizer(x)
 
 ##############################
 # Helpers for binary codes
diff --git a/test/test_stabs.jl b/test/test_stabs.jl
index 1324c22d3..d415621ea 100644
--- a/test/test_stabs.jl
+++ b/test/test_stabs.jl
@@ -61,9 +61,6 @@
             @test mixed_destab_looks_good(mds)
             estab = stabilizerview(md)⊗s
             @test canonicalize!(copy(stabilizerview(mds))) == canonicalize!(estab)
-            d = random_destabilizer(n)
-            sd = random_stabilizer(n)⊗random_destabilizer(n)
-            @test mixed_destab_looks_good(sd)
         end
     end