diff --git a/src/monomial.jl b/src/monomial.jl
index 8c99ad0..13ae659 100644
--- a/src/monomial.jl
+++ b/src/monomial.jl
@@ -423,10 +423,11 @@ function SA.coeffs(
         # The defaults initialize to zero and then sums which promotes
         # `JuMP.VariableRef` to `JuMP.AffExpr`
         return SA.SparseCoefficients(_vec(source.monomials), _vec(cfs))
-    elseif B2 === Monomial
-        res = SA.zero_coeffs(_promote_coef(valtype(cfs), B1), target)
-        return SA.coeffs!(res, cfs, source, target)
     else
-        error("Convertion from `$source` to `$target` not implemented yet")
+        res = SA.zero_coeffs(
+            _promote_coef(_promote_coef(valtype(cfs), B1), B2),
+            target,
+        )
+        return SA.coeffs!(res, cfs, source, target)
     end
 end
diff --git a/test/hermite.jl b/test/hermite.jl
index c72c97e..cd28b62 100644
--- a/test/hermite.jl
+++ b/test/hermite.jl
@@ -48,8 +48,4 @@ end
     M = typeof(x^2)
     mono = MB.FullBasis{MB.Monomial,M}()
     basis = MB.FullBasis{MB.PhysicistsHermite,M}()
-    err = ErrorException(
-        "Convertion from `$mono` to `$basis` not implemented yet",
-    )
-    @test_throws err SA.coeffs(MB.algebra_element(x + 1), basis)
 end
diff --git a/test/scaled.jl b/test/scaled.jl
index 77d4ae5..4975b21 100644
--- a/test/scaled.jl
+++ b/test/scaled.jl
@@ -20,7 +20,13 @@ end
     basis = MB.SubBasis{MB.ScaledMonomial}([x^2, x * y, y^2])
     @test polynomial_type(basis, Int) == polynomial_type(x, Float64)
     @test polynomial(i -> i^2, basis) == 9x^2 + 4 * √2 * x * y + y^2
-    @test coefficients(x^2 + 4x * y + 9y^2, basis) == [9, 4 / √2, 1]
+    p = x^2 + 4x * y + 9y^2
+    @test coefficients(p, basis) == [9, 4 / √2, 1]
+    a = MB.algebra_element(p)
+    @test SA.coeffs(a, basis) == [9, 4 / √2, 1]
+    full = MB.FullBasis{MB.ScaledMonomial,monomial_type(p)}()
+    @test SA.coeffs(a, full) ==
+          SA.SparseCoefficients([y^2, x * y, x^2], [9, 4 / √2, 1])
     @test polynomial(basis[1]) == y^2
     @test polynomial(basis[2]) == √2 * x * y
     @test polynomial(basis[3]) == x^2