diff --git a/base/compiler/abstractinterpretation.jl b/base/compiler/abstractinterpretation.jl
index 65134bacc422f..8c8f868b2ed8b 100644
--- a/base/compiler/abstractinterpretation.jl
+++ b/base/compiler/abstractinterpretation.jl
@@ -1498,20 +1498,26 @@ function abstract_call_builtin(interp::AbstractInterpreter, f::Builtin, (; fargs
             if isa(aty, Const) && isa(b, SlotNumber)
                 if rt === Const(false)
                     aty = Union{}
+                    bty = widenconditional(bty)
                 elseif rt === Const(true)
                     bty = Union{}
                 elseif bty isa Type && isdefined(typeof(aty.val), :instance) # can only widen a if it is a singleton
                     bty = typesubtract(bty, typeof(aty.val), InferenceParams(interp).MAX_UNION_SPLITTING)
+                else
+                    bty = widenconditional(bty)
                 end
                 return Conditional(b, aty, bty)
             end
             if isa(bty, Const) && isa(a, SlotNumber)
                 if rt === Const(false)
                     bty = Union{}
+                    aty = widenconditional(aty)
                 elseif rt === Const(true)
                     aty = Union{}
                 elseif aty isa Type && isdefined(typeof(bty.val), :instance) # same for b
                     aty = typesubtract(aty, typeof(bty.val), InferenceParams(interp).MAX_UNION_SPLITTING)
+                else
+                    aty = widenconditional(aty)
                 end
                 return Conditional(a, bty, aty)
             end
diff --git a/test/compiler/inference.jl b/test/compiler/inference.jl
index 77b74969b099b..972cc9f188edc 100644
--- a/test/compiler/inference.jl
+++ b/test/compiler/inference.jl
@@ -2102,6 +2102,16 @@ let M = Module()
     @test rt == Tuple{Union{Nothing,Int},Any}
 end
 
+# make sure we never form nested `Conditional` (https://github.com/JuliaLang/julia/issues/46207)
+@test Base.return_types((Any,)) do a
+    c = isa(a, Integer)
+    42 === c ? :a : "b"
+end |> only === String
+@test Base.return_types((Any,)) do a
+    c = isa(a, Integer)
+    c === 42 ? :a : "b"
+end |> only === String
+
 @testset "conditional constraint propagation from non-`Conditional` object" begin
     @test Base.return_types((Bool,)) do b
         if b