diff --git a/src/datatype.c b/src/datatype.c
index b3ff1997ca8eb..9cf1ec58e09e9 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -19,6 +19,11 @@ extern "C" {
 
 // allocating TypeNames -----------------------------------------------------------
 
+static int is10digit(char c) JL_NOTSAFEPOINT
+{
+    return (c >= '0' && c <= '9');
+}
+
 jl_sym_t *jl_demangle_typename(jl_sym_t *s) JL_NOTSAFEPOINT
 {
     char *n = jl_symbol_name(s);
@@ -30,6 +35,8 @@ jl_sym_t *jl_demangle_typename(jl_sym_t *s) JL_NOTSAFEPOINT
         len = strlen(n) - 1;
     else
         len = (end-n) - 1;  // extract `f` from `#f#...`
+    if (is10digit(n[1]))
+        return jl_symbol_n(n, len+1);
     return jl_symbol_n(&n[1], len);
 }
 
@@ -448,6 +455,14 @@ void jl_compute_field_offsets(jl_datatype_t *st)
     jl_errorf("type %s has field offset %d that exceeds the page size", jl_symbol_name(st->name->name), descsz);
 }
 
+static int is_anonfn_typename(char *name)
+{
+    if (name[0] != '#')
+        return 0;
+    char *other = strrchr(name, '#');
+    return (name[1] != '#' && other > &name[1] && is10digit(other[1]));
+}
+
 JL_DLLEXPORT jl_datatype_t *jl_new_datatype(
         jl_sym_t *name,
         jl_module_t *module,
@@ -487,7 +502,7 @@ JL_DLLEXPORT jl_datatype_t *jl_new_datatype(
     }
     else {
         tn = jl_new_typename_in((jl_sym_t*)name, module);
-        if (super == jl_function_type || super == jl_builtin_type || jl_symbol_name(name)[0] == '#') {
+        if (super == jl_function_type || super == jl_builtin_type || is_anonfn_typename(jl_symbol_name(name))) {
             // Callable objects (including compiler-generated closures) get independent method tables
             // as an optimization
             tn->mt = jl_new_method_table(name, module);
diff --git a/src/julia-syntax.scm b/src/julia-syntax.scm
index 46d7054389e21..ac477a9966ac3 100644
--- a/src/julia-syntax.scm
+++ b/src/julia-syntax.scm
@@ -435,8 +435,12 @@
                   sparams)))
     (let ((kw      (gensy))
           (rkw     (if (null? restkw) (make-ssavalue) (symbol (string (car restkw) "..."))))
-          (mangled (symbol (string (if name (undot-name name) '_) "#"
-                                   (current-julia-module-counter)))))
+          (mangled (let ((und (and name (undot-name name))))
+                     (symbol (string (if (and name (= (string.char (string name) 0) #\#))
+                                         ""
+                                         "#")
+                                     (or und '_) "#"
+                                     (string (current-julia-module-counter)))))))
       ;; this is a hack: nest these statements inside a call so they get closure
       ;; converted together, allowing all needed types to be defined before any methods.
       `(call (core ifelse) false false (block
@@ -3265,7 +3269,10 @@ f(x) = yt(x)
                  (let* ((exists (get defined name #f))
                         (type-name  (or (get namemap name #f)
                                         (and name
-                                             (symbol (string "#" name "#" (current-julia-module-counter))))))
+                                             (symbol (string (if (= (string.char (string name) 0) #\#)
+                                                                 ""
+                                                                 "#")
+                                                             name "#" (current-julia-module-counter))))))
                         (alldefs (expr-find-all
                                   (lambda (ex) (and (length> ex 2) (eq? (car ex) 'method)
                                                     (not (eq? ex e))
diff --git a/test/core.jl b/test/core.jl
index 0d6b99c73ee6e..ec5de14031b7d 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -2404,6 +2404,20 @@ for f in (:(Core.arrayref), :((::typeof(Core.arrayref))), :((::Core.IntrinsicFun
     @test_throws ErrorException("cannot add methods to a builtin function") @eval $f() = 1
 end
 
+# issue #33370
+abstract type B33370 end
+
+let n = gensym(), c(x) = B33370[x][1]()
+    @eval begin
+        struct $n <: B33370
+        end
+
+        function (::$n)()
+        end
+    end
+    @test c(eval(n)()) === nothing
+end
+
 # issue #8798
 let
     npy_typestrs = Dict("b1"=>Bool,