diff --git a/src/coefficients.jl b/src/coefficients.jl
index 735be39..f7fd687 100644
--- a/src/coefficients.jl
+++ b/src/coefficients.jl
@@ -48,30 +48,25 @@ If `ac` can be brought to canonical form in-place one has to implement
 
 otherwise `canonical(ac)` needs to be implemented.
 """
-canonical(ac::AbstractCoefficients) = ac
-MA.operate(::typeof(canonical), x) = canonical(x) # fallback?
+function canonical end
+function MA.promote_operation(::typeof(canonical), ::Type{C}) where {C}
+    return C
+end
 
 # example implementation for vectors
-function MA.mutability(
-    ::Type{<:Union{<:SparseVector,<:Vector}},
-    ::typeof(canonical),
-    ::Vararg{Type},
-)
-    return MA.IsMutable()
-end
 MA.operate!(::typeof(canonical), sv::SparseVector) = dropzeros!(sv)
 MA.operate!(::typeof(canonical), v::Vector) = v
 
 function Base.:(==)(ac1::AbstractCoefficients, ac2::AbstractCoefficients)
-    ac1 = MA.operate!!(canonical, ac1)
-    ac2 = MA.operate!!(canonical, ac2)
+    MA.operate!(canonical, ac1)
+    MA.operate!(canonical, ac2)
     all(x -> ==(x...), zip(keys(ac1), keys(ac2))) || return false
     all(x -> ==(x...), zip(values(ac1), values(ac2))) || return false
     return true
 end
 
 function Base.hash(ac::AbstractCoefficients, h::UInt)
-    ac = MA.operate!!(canonical, ac)
+    MA.operate!(canonical, ac)
     return foldl((h, i) -> hash(i, h), nonzero_pairs(ac); init = h)
 end
 
diff --git a/src/diracs_augmented.jl b/src/diracs_augmented.jl
index 904a874..e555472 100644
--- a/src/diracs_augmented.jl
+++ b/src/diracs_augmented.jl
@@ -18,7 +18,7 @@ function Base.getindex(aδ::Augmented{K}, i::K) where {K}
     return zero(w)
 end
 
-canonical(aδ::Augmented) = aδ
+MA.operate!(::typeof(canonical), aδ::Augmented) = aδ
 
 Base.keys(aδ::Augmented) = (k = keys(aδ.elt); (one(first(k)), first(k)))
 function Base.values(aδ::Augmented)
@@ -129,5 +129,6 @@ function coeffs!(
             SparseCoefficients((target[Augmented(x)],), (1,)),
         )
     end
-    return MA.operate!!(canonical, res)
+    MA.operate!(canonical, res)
+    return res
 end
diff --git a/src/mstructures.jl b/src/mstructures.jl
index d0fc193..2cf3e73 100644
--- a/src/mstructures.jl
+++ b/src/mstructures.jl
@@ -49,8 +49,9 @@ function MA.operate_to!(res, ms::MultiplicativeStructure, v, w)
         throw(ArgumentError("No alias allowed"))
     end
     MA.operate!(zero, res)
-    res = MA.operate!(UnsafeAddMul(ms), res, v, w)
-    return MA.operate!!(canonical, res)
+    MA.operate!(UnsafeAddMul(ms), res, v, w)
+    MA.operate!(canonical, res)
+    return res
 end
 
 function MA.operate!(
diff --git a/test/test_example_acoeffs.jl b/test/test_example_acoeffs.jl
index 3a21966..2c9272f 100644
--- a/test/test_example_acoeffs.jl
+++ b/test/test_example_acoeffs.jl
@@ -10,7 +10,7 @@ ACoeffs(v::AbstractVector) = ACoeffs{valtype(v)}(v)
 ## Basic API
 Base.keys(ac::ACoeffs) = (k for (k, v) in pairs(ac.vals) if !iszero(v))
 Base.values(ac::ACoeffs) = (v for v in ac.vals if !iszero(v))
-SA.canonical(ac::ACoeffs) = ac
+MA.operate!(::typeof(SA.canonical), ac::ACoeffs) = ac
 function SA.star(b::SA.AbstractBasis, ac::ACoeffs)
     return ACoeffs([ac.vals[star(b, k)] for k in keys(ac)])
 end