diff --git a/base/sysimg.jl b/base/sysimg.jl
index ee4f6474ed40a..76e328df54e21 100644
--- a/base/sysimg.jl
+++ b/base/sysimg.jl
@@ -100,3 +100,6 @@ end
 
 empty!(LOAD_PATH)
 empty!(DEPOT_PATH)
+
+# Set up Main module
+import Base.MainInclude: eval, include
diff --git a/src/dump.c b/src/dump.c
index f4d2cbb25a28a..da73b71c7eab5 100644
--- a/src/dump.c
+++ b/src/dump.c
@@ -453,30 +453,22 @@ static void jl_serialize_module(jl_serializer_state *s, jl_module_t *m)
     for (i = 1; i < m->bindings.size; i += 2) {
         if (table[i] != HT_NOTFOUND) {
             jl_binding_t *b = (jl_binding_t*)table[i];
-            if (b->owner == m || m != jl_main_module) {
-                jl_serialize_value(s, b->name);
-                jl_value_t *e = b->value;
-                if (!b->constp && e && jl_is_cpointer(e) && jl_unbox_voidpointer(e) != (void*)-1 && jl_unbox_voidpointer(e) != NULL)
-                    // reset Ptr fields to C_NULL (but keep MAP_FAILED / INVALID_HANDLE)
-                    jl_serialize_cnull(s, jl_typeof(e));
-                else
-                    jl_serialize_value(s, e);
-                jl_serialize_value(s, b->globalref);
-                jl_serialize_value(s, b->owner);
-                write_int8(s->s, (b->deprecated<<3) | (b->constp<<2) | (b->exportp<<1) | (b->imported));
-            }
+            jl_serialize_value(s, b->name);
+            jl_value_t *e = b->value;
+            if (!b->constp && e && jl_is_cpointer(e) && jl_unbox_voidpointer(e) != (void*)-1 && jl_unbox_voidpointer(e) != NULL)
+                // reset Ptr fields to C_NULL (but keep MAP_FAILED / INVALID_HANDLE)
+                jl_serialize_cnull(s, jl_typeof(e));
+            else
+                jl_serialize_value(s, e);
+            jl_serialize_value(s, b->globalref);
+            jl_serialize_value(s, b->owner);
+            write_int8(s->s, (b->deprecated<<3) | (b->constp<<2) | (b->exportp<<1) | (b->imported));
         }
     }
     jl_serialize_value(s, NULL);
-    if (m == jl_main_module) {
-        write_int32(s->s, 1);
-        jl_serialize_value(s, (jl_value_t*)jl_core_module);
-    }
-    else {
-        write_int32(s->s, m->usings.len);
-        for(i=0; i < m->usings.len; i++) {
-            jl_serialize_value(s, (jl_value_t*)m->usings.items[i]);
-        }
+    write_int32(s->s, m->usings.len);
+    for(i=0; i < m->usings.len; i++) {
+        jl_serialize_value(s, (jl_value_t*)m->usings.items[i]);
     }
     write_uint8(s->s, m->istopmod);
     write_uint64(s->s, m->uuid.hi);
diff --git a/src/init.c b/src/init.c
index 4497a21479be3..7ac804ba6f5d4 100644
--- a/src/init.c
+++ b/src/init.c
@@ -738,6 +738,7 @@ void _julia_init(JL_IMAGE_SEARCH rel)
 
     if (!jl_options.image_file) {
         jl_core_module = jl_new_module(jl_symbol("Core"));
+        jl_core_module->parent = jl_core_module;
         jl_type_typename->mt->module = jl_core_module;
         jl_top_module = jl_core_module;
         jl_init_intrinsic_functions();
@@ -747,16 +748,7 @@ void _julia_init(JL_IMAGE_SEARCH rel)
         post_boot_hooks();
     }
 
-    // the Main module is the one which is always open, and set as the
-    // current module for bare (non-module-wrapped) toplevel expressions.
-    // it does "using Base" if Base is available.
     if (jl_base_module != NULL) {
-        jl_add_standard_imports(jl_main_module);
-        jl_value_t *maininclude = jl_get_global(jl_base_module, jl_symbol("MainInclude"));
-        if (maininclude && jl_is_module(maininclude)) {
-            jl_module_import(jl_main_module, (jl_module_t*)maininclude, jl_symbol("include"));
-            jl_module_import(jl_main_module, (jl_module_t*)maininclude, jl_symbol("eval"));
-        }
         // Do initialization needed before starting child threads
         jl_value_t *f = jl_get_global(jl_base_module, jl_symbol("__preinit_threads__"));
         if (f) {
diff --git a/src/staticdata.c b/src/staticdata.c
index 54e8db3042286..fb9eaa98510cc 100644
--- a/src/staticdata.c
+++ b/src/staticdata.c
@@ -262,19 +262,15 @@ static void jl_serialize_module(jl_serializer_state *s, jl_module_t *m)
     for (i = 1; i < m->bindings.size; i += 2) {
         if (table[i] != HT_NOTFOUND) {
             jl_binding_t *b = (jl_binding_t*)table[i];
-            if (b->owner == m || m != jl_main_module) {
-                jl_serialize_value(s, b->name);
-                jl_serialize_value(s, b->value);
-                jl_serialize_value(s, b->globalref);
-                jl_serialize_value(s, b->owner);
-            }
+            jl_serialize_value(s, b->name);
+            jl_serialize_value(s, b->value);
+            jl_serialize_value(s, b->globalref);
+            jl_serialize_value(s, b->owner);
         }
     }
 
-    if (m != jl_main_module) {
-        for (i = 0; i < m->usings.len; i++) {
-            jl_serialize_value(s, (jl_value_t*)m->usings.items[i]);
-        }
+    for (i = 0; i < m->usings.len; i++) {
+        jl_serialize_value(s, (jl_value_t*)m->usings.items[i]);
     }
 }
 
@@ -495,65 +491,50 @@ static void jl_write_module(jl_serializer_state *s, uintptr_t item, jl_module_t
     for (i = 1; i < m->bindings.size; i += 2) {
         if (table[i] != HT_NOTFOUND) {
             jl_binding_t *b = (jl_binding_t*)table[i];
-            if (b->owner == m || m != jl_main_module) {
-                write_gctaggedfield(s, (uintptr_t)BindingRef << RELOC_TAG_OFFSET);
-                tot += sizeof(void*);
-                size_t binding_reloc_offset = ios_pos(s->s);
-                record_gvar(s, jl_get_llvm_gv((jl_value_t*)b), ((uintptr_t)DataRef << RELOC_TAG_OFFSET) + binding_reloc_offset);
-                write_pointerfield(s, (jl_value_t*)b->name);
-                write_pointerfield(s, b->value);
-                write_pointerfield(s, b->globalref);
-                write_pointerfield(s, (jl_value_t*)b->owner);
-                size_t flag_offset = offsetof(jl_binding_t, owner) + sizeof(b->owner);
-                ios_write(s->s, (char*)b + flag_offset, sizeof(*b) - flag_offset);
-                tot += sizeof(jl_binding_t);
-                count += 1;
-            }
+            write_gctaggedfield(s, (uintptr_t)BindingRef << RELOC_TAG_OFFSET);
+            tot += sizeof(void*);
+            size_t binding_reloc_offset = ios_pos(s->s);
+            record_gvar(s, jl_get_llvm_gv((jl_value_t*)b), ((uintptr_t)DataRef << RELOC_TAG_OFFSET) + binding_reloc_offset);
+            write_pointerfield(s, (jl_value_t*)b->name);
+            write_pointerfield(s, b->value);
+            write_pointerfield(s, b->globalref);
+            write_pointerfield(s, (jl_value_t*)b->owner);
+            size_t flag_offset = offsetof(jl_binding_t, owner) + sizeof(b->owner);
+            ios_write(s->s, (char*)b + flag_offset, sizeof(*b) - flag_offset);
+            tot += sizeof(jl_binding_t);
+            count += 1;
         }
     }
     assert(ios_pos(s->s) - reloc_offset == tot);
-    newm = (jl_module_t*)&s->s->buf[reloc_offset];
+    newm = (jl_module_t*)&s->s->buf[reloc_offset]; // buf might have been reallocated
     newm->bindings.size = count; // stash the count in newm->size
     newm->bindings.table = NULL;
     memset(&newm->bindings._space, 0, sizeof(newm->bindings._space));
 
     // write out the usings list
     memset(&newm->usings._space, 0, sizeof(newm->usings._space));
-    if (m == jl_main_module) {
-        newm->usings.len = 1;
-        newm->usings.max = AL_N_INLINE;
+    if (m->usings.items == &m->usings._space[0]) {
         newm->usings.items = (void**)offsetof(jl_module_t, usings._space);
         arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings.items)));
         arraylist_push(&s->relocs_list, (void*)(((uintptr_t)DataRef << RELOC_TAG_OFFSET) + item));
-        arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings._space[0])));
-        arraylist_push(&s->relocs_list, (void*)backref_id(s, jl_core_module));
+        size_t i;
+        for (i = 0; i < m->usings.len; i++) {
+            arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings._space[i])));
+            arraylist_push(&s->relocs_list, (void*)backref_id(s, m->usings._space[i]));
+        }
     }
     else {
-        if (newm->usings.items == &newm->usings._space[0]) {
-            m->usings.max = AL_N_INLINE;
-            newm->usings.items = (void**)offsetof(jl_module_t, usings._space);
-            arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings.items)));
-            arraylist_push(&s->relocs_list, (void*)(((uintptr_t)DataRef << RELOC_TAG_OFFSET) + item));
-            size_t i;
-            for (i = 0; i < m->usings.len; i++) {
-                arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings._space[i])));
-                arraylist_push(&s->relocs_list, (void*)backref_id(s, m->usings._space[i]));
-            }
+        newm->usings.items = (void**)tot;
+        arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings.items)));
+        arraylist_push(&s->relocs_list, (void*)(((uintptr_t)DataRef << RELOC_TAG_OFFSET) + item));
+        size_t i;
+        for (i = 0; i < m->usings.len; i++) {
+            write_pointerfield(s, (jl_value_t*)m->usings.items[i]);
+            tot += sizeof(void*);
         }
-        else {
-            newm->usings.items = (void**)tot;
-            arraylist_push(&s->relocs_list, (void*)(reloc_offset + offsetof(jl_module_t, usings.items)));
-            arraylist_push(&s->relocs_list, (void*)(((uintptr_t)DataRef << RELOC_TAG_OFFSET) + item));
-            size_t i;
-            for (i = 0; i < m->usings.len; i++) {
-                write_pointerfield(s, (jl_value_t*)m->usings.items[i]);
-                tot += sizeof(void*);
-            }
-            for (; i < m->usings.max; i++) {
-                write_pointer(s->s);
-                tot += sizeof(void*);
-            }
-            // newm = (jl_module_t*)&s->s->buf[reloc_offset];
+        for (; i < m->usings.max; i++) {
+            write_pointer(s->s);
+            tot += sizeof(void*);
         }
     }
 }
@@ -1265,6 +1246,11 @@ static void jl_reinit_item(jl_value_t *v, int how)
                 b += 1;
                 nbindings -= 1;
             }
+            if (mod->usings.items != &mod->usings._space[0]) {
+                void **newitems = (void**)malloc_s(mod->usings.max * sizeof(void*));
+                memcpy(newitems, mod->usings.items, mod->usings.len * sizeof(void*));
+                mod->usings.items = newitems;
+            }
             break;
         }
         default:
diff --git a/src/toplevel.c b/src/toplevel.c
index 12d688d468160..17dd9f046d576 100644
--- a/src/toplevel.c
+++ b/src/toplevel.c
@@ -49,7 +49,6 @@ void jl_init_main_module(void)
 
     jl_main_module = jl_new_module(jl_symbol("Main"));
     jl_main_module->parent = jl_main_module;
-    jl_core_module->parent = jl_main_module;
     jl_set_const(jl_main_module, jl_symbol("Core"),
                  (jl_value_t*)jl_core_module);
     jl_set_global(jl_core_module, jl_symbol("Main"),
diff --git a/stdlib/Test/src/Test.jl b/stdlib/Test/src/Test.jl
index 0600dbff0bb0b..3fb64bdff5bd3 100644
--- a/stdlib/Test/src/Test.jl
+++ b/stdlib/Test/src/Test.jl
@@ -1491,7 +1491,7 @@ function detect_unbound_args(mods...;
                 continue
             end
             f = Base.unwrap_unionall(getfield(mod, n))
-            if recursive && isa(f, Module) && parentmodule(f) === mod && nameof(f) === n
+            if recursive && isa(f, Module) && f !== mod && parentmodule(f) === mod && nameof(f) === n
                 subambs = detect_unbound_args(f, imported=imported, recursive=recursive)
                 union!(ambs, subambs)
             elseif isa(f, DataType) && isdefined(f.name, :mt)