diff --git a/base/compiler/ssair/passes.jl b/base/compiler/ssair/passes.jl
index 34c69dcc2dc2ef..efacbf4ca219b7 100644
--- a/base/compiler/ssair/passes.jl
+++ b/base/compiler/ssair/passes.jl
@@ -537,7 +537,7 @@ function getfield_elim_pass!(ir::IRCode)
         elseif is_known_call(stmt, isa, compact)
             # TODO
             continue
-        elseif is_known_call(stmt, typeassert, compact)
+        elseif is_known_call(stmt, typeassert, compact) && length(stmt.args) == 3
             # Canonicalize
             #   X = typeassert(Y, T)::S
             # into
@@ -557,7 +557,7 @@ function getfield_elim_pass!(ir::IRCode)
                 compact.result[idx][:line], true)
             compact.ssa_rename[compact.idx-1] = pi
             continue
-        elseif is_known_call(stmt, (===), compact)
+        elseif is_known_call(stmt, (===), compact) && length(stmt.args) == 3
             c1 = compact_exprtype(compact, stmt.args[2])
             c2 = compact_exprtype(compact, stmt.args[3])
             if !(isa(c1, Const) || isa(c2, Const))
diff --git a/test/compiler/inference.jl b/test/compiler/inference.jl
index 2540d3c870e73d..d13d73ec6f10c6 100644
--- a/test/compiler/inference.jl
+++ b/test/compiler/inference.jl
@@ -2990,3 +2990,7 @@ f28971() = (1, [2,3]...)::Tuple{Int,Int,Int}
 let f() = sin{Int}()
     @test Base.return_types(f, ()) == Any[Union{}]
 end
+
+# issue #40804
+@test Base.return_types(()) do; ===(); end == Any[Union{}]
+@test Base.return_types(()) do; typeassert(); end == Any[Union{}]