diff --git a/src/toplevel.c b/src/toplevel.c
index 0b752fb1c161e..6f29c0a82d617 100644
--- a/src/toplevel.c
+++ b/src/toplevel.c
@@ -874,8 +874,9 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
     int has_ccall = 0, has_defs = 0, has_loops = 0, has_opaque = 0, forced_compile = 0;
     assert(head == jl_thunk_sym);
     thk = (jl_code_info_t*)jl_exprarg(ex, 0);
-    assert(jl_is_code_info(thk));
-    assert(jl_typeis(thk->code, jl_array_any_type));
+    if (!jl_is_code_info(thk) || !jl_typeis(thk->code, jl_array_any_type)) {
+        jl_eval_errorf(m, "malformed \"thunk\" statement");
+    }
     body_attributes((jl_array_t*)thk->code, &has_ccall, &has_defs, &has_loops, &has_opaque, &forced_compile);
 
     jl_value_t *result;
diff --git a/test/syntax.jl b/test/syntax.jl
index 2410e5c8a8b62..32f343f4a392e 100644
--- a/test/syntax.jl
+++ b/test/syntax.jl
@@ -2330,7 +2330,7 @@ f35201(c) = h35201((;c...), k=true)
 f44343(;kw...) = NamedTuple(kw)
 @test f44343(u = (; :a => 1)) === (u = (; :a => 1),)
 
-@testset "issue #34544/35367" begin
+@testset "issue #34544/35367/35429" begin
     # Test these evals shouldn't segfault
     eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar1, Expr(:block)))))
     eval(Expr(:module, true, :bar2, Expr(:block)))
@@ -2338,6 +2338,11 @@ f44343(;kw...) = NamedTuple(kw)
     @test_throws ErrorException eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar4, Expr(:quote)))))
     @test_throws ErrorException eval(Expr(:module, true, :bar5, Expr(:foo)))
     @test_throws ErrorException eval(Expr(:module, true, :bar6, Expr(:quote)))
+
+    #35429
+    @test_throws ErrorException eval(Expr(:thunk, x->x+9))
+    @test_throws ErrorException eval(Expr(:thunk, Meta.parse("x=17")))
+    @test_throws ErrorException eval(Expr(:thunk, Meta.parse("17")))
 end
 
 # issue #35391