diff --git a/src/cmult.jl b/src/cmult.jl
index aea7228..acc5a77 100644
--- a/src/cmult.jl
+++ b/src/cmult.jl
@@ -28,13 +28,7 @@ function _operate_exponents_to!(output::Vector{Int}, op::F, z1::Vector{Int}, z2:
     @. output = op(z1, z2)
     return
 end
-function _operate_exponents_to!(output::Vector{Int}, op::F, z1::Vector{Int}, z2::Vector{Int}, n) where {F<:Function}
-    resize!(output, n)
-    @. output = op(z1, z2)
-    return
-end
-function _operate_exponents_to!(output::Vector{Int}, op::F, z1::Vector{Int}, z2::Vector{Int}, n, maps) where {F<:Function}
-    resize!(output, n)
+function _operate_exponents_to!(output::Vector{Int}, op::F, z1::Vector{Int}, z2::Vector{Int}, maps) where {F<:Function}
     I = maps[1]; i = 1; lI = length(I)
     J = maps[2]; j = 1; lJ = length(J)
     while i <= lI || j <= lJ
@@ -42,11 +36,11 @@ function _operate_exponents_to!(output::Vector{Int}, op::F, z1::Vector{Int}, z2:
             output[J[j]] = op(0, z2[j])
             j += 1
         elseif j > lJ || (i <= lI && I[i] < J[j])
-            output[I[i]] = op(z1[I[i]], 0)
+            output[I[i]] = op(z1[i], 0)
             i += 1
         else
             @assert I[i] == J[j]
-            output[I[i]] = op(z1[I[i]], z2[j])
+            output[I[i]] = op(z1[i], z2[j])
             i += 1
             j += 1
         end
@@ -57,19 +51,19 @@ end
 #function _operate_exponents!(op::F, Z::Vector{Vector{Int}}, z2::Vector{Int}, args::Vararg{Any,N}) where {F<:Function,N}
 #    return Vector{Int}[_operate_exponents!(op, z, z2, args...) for z in Z]
 #end
-function multdivmono!(output, output_variables::Vector{PolyVar{true}},
+function _multdivmono!(output, output_variables::Vector{PolyVar{true}},
                       v::Vector{PolyVar{true}}, x::Monomial{true}, op, z)
     if v == x.vars
-        if output_variables == v
-            _operate_exponents_to!(output, op, z, x.z)
-        else
+        if output_variables != v
             resize!(output_variables, length(v))
             copyto!(output_variables, v)
-            _operate_exponents_to!(output, op, z, x.z, length(output_variables))
+            resize!(output, length(output_variables))
         end
+        _operate_exponents_to!(output, op, z, x.z)
     else
         maps = mergevars_to!(output_variables, [v, x.vars])
-        _operate_exponents_to!(output, op, z, x.z, length(output_variables), maps)
+        resize!(output, length(output_variables))
+        _operate_exponents_to!(output, op, z, x.z, maps)
     end
     return
 end
@@ -110,11 +104,25 @@ function multdivmono(v::Vector{PolyVar{true}}, x::Monomial{true}, op, z)
     return w, z_new
 end
 function MP.mapexponents_to!(output::Monomial{true}, f::Function, x::Monomial{true}, y::Monomial{true})
-    multdivmono!(output.z, output.vars, x.vars, y, f, x.z)
+    if x.vars == y.vars
+        if output.vars != x.vars
+            n = length(x.vars)
+            resize!(output.vars, n)
+            copyto!(output.vars, x.vars)
+            resize!(output.z, n)
+        end
+        _operate_exponents_to!(x.z, f, x.z, y.z)
+    else
+        _multdivmono!(output.z, output.vars, x.vars, y, f, x.z)
+    end
     return output
 end
 function MP.mapexponents!(f::Function, x::Monomial{true}, y::Monomial{true})
-    multdivmono!(x.z, x.vars, x.vars, y, f, x.z)
+    if x.vars == y.vars
+        _operate_exponents_to!(x.z, f, x.z, y.z)
+    else
+        _multdivmono!(x.z, x.vars, copy(x.vars), y, f, copy(x.z))
+    end
     return x
 end
 function MP.mapexponents(f::Function, x::Monomial{true}, y::Monomial{true})
diff --git a/test/mono.jl b/test/mono.jl
index a7f7d01..89b60aa 100644
--- a/test/mono.jl
+++ b/test/mono.jl
@@ -133,4 +133,8 @@
         @test (x^2)(3) == 9
         @test (x)(3) == 3
     end
+    @testset "TODO remove when added to MP" begin
+        @polyvar x y
+        @test x == DynamicPolynomials.MP.mapexponents!(div, x^1, x * y^2)
+    end
 end