diff --git a/src/builtins.c b/src/builtins.c
index ccf1a016d6111..aaec4de02fa66 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -1005,6 +1005,12 @@ JL_CALLABLE(jl_f_union)
 
 // generic function reflection ------------------------------------------------
 
+static void jl_check_type_tuple(jl_value_t *t, jl_sym_t *name, const char *ctx)
+{
+    if (!jl_is_tuple_type(t))
+        jl_type_error_rt(name->name, ctx, (jl_value_t*)jl_type_type, t);
+}
+
 JL_CALLABLE(jl_f_methodexists)
 {
     JL_NARGS(method_exists, 2, 2);
diff --git a/src/interpreter.c b/src/interpreter.c
index 2f4494fc7030c..46006808a84d2 100644
--- a/src/interpreter.c
+++ b/src/interpreter.c
@@ -410,7 +410,11 @@ static jl_value_t *eval(jl_value_t *e, jl_value_t **locals, size_t nl, size_t ng
             dt->types = (jl_svec_t*)eval(args[4], locals, nl, ngensym);
             gc_wb(dt, dt->types);
             inside_typedef = 0;
-            //jl_check_type_tuple(dt->types, dt->name->name, "type definition");
+            for(size_t i=0; i < jl_svec_len(dt->types); i++) {
+                jl_value_t *elt = jl_svecref(dt->types, i);
+                if (!jl_is_type(elt) && !jl_is_typevar(elt))
+                    jl_type_error_rt(dt->name->name->name, "type definition", (jl_value_t*)jl_type_type, elt);
+            }
             super = eval(args[3], locals, nl, ngensym);
             jl_set_datatype_super(dt, super);
         }
diff --git a/src/julia_internal.h b/src/julia_internal.h
index a75feae456d1a..0115aa09bad61 100644
--- a/src/julia_internal.h
+++ b/src/julia_internal.h
@@ -49,7 +49,6 @@ uint32_t jl_get_gs_ctr(void);
 void jl_set_gs_ctr(uint32_t ctr);
 
 void NORETURN jl_no_method_error(jl_function_t *f, jl_value_t **args, size_t na);
-void jl_check_type_tuple(jl_value_t *t, jl_sym_t *name, const char *ctx);
 
 #define JL_CALLABLE(name) \
     DLLEXPORT jl_value_t *name(jl_value_t *F, jl_value_t **args, uint32_t nargs)
diff --git a/src/toplevel.c b/src/toplevel.c
index 453872696c869..ff115071e8fa8 100644
--- a/src/toplevel.c
+++ b/src/toplevel.c
@@ -613,12 +613,6 @@ DLLEXPORT jl_value_t *jl_load_(jl_value_t *str)
 
 void jl_reinstantiate_inner_types(jl_datatype_t *t);
 
-void jl_check_type_tuple(jl_value_t *t, jl_sym_t *name, const char *ctx)
-{
-    if (!jl_is_tuple_type(t))
-        jl_type_error_rt(name->name, ctx, (jl_value_t*)jl_type_type, t);
-}
-
 void jl_set_datatype_super(jl_datatype_t *tt, jl_value_t *super)
 {
     if (!jl_is_datatype(super) || !jl_is_abstracttype(super) ||