3 files changed, 23 insertions, 0 deletions
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 2d888862bf..fbdddf09db 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -157,6 +157,7 @@ bif erts_internal:binary_to_term/2
 bif erts_internal:request_system_task/3
 bif erts_internal:check_process_code/2
 
+bif erts_internal:map_to_tuple_keys/1
 
 # inet_db support
 bif erlang:port_set_data/2
diff --git a/erts/emulator/beam/erl_map.c b/erts/emulator/beam/erl_map.c
index fdd2d0c0f6..5e740aacdd 100644
--- a/erts/emulator/beam/erl_map.c
+++ b/erts/emulator/beam/erl_map.c
@@ -58,6 +58,8 @@
  * - maps:size/1
  * - maps:without/2
  *
+ * DEBUG: for sharing calculation
+ * - erts_internal:map_to_tuple_keys/1
  */
 
 /* erlang:map_size/1
@@ -819,3 +821,17 @@ int erts_validate_and_sort_map(map_t* mp)
     }
     return 1;
 }
+
+/*
+ * erts_internal:map_to_tuple_keys/1
+ *
+ * Used in erts_debug:size/1
+ */
+
+BIF_RETTYPE erts_internal_map_to_tuple_keys_1(BIF_ALIST_1) {
+    if (is_map(BIF_ARG_1)) {
+	map_t *mp = (map_t*)map_val(BIF_ARG_1);
+	BIF_RET(mp->keys);
+    }
+    BIF_ERROR(BIF_P, BADARG);
+}
diff --git a/erts/emulator/test/erts_debug_SUITE.erl b/erts/emulator/test/erts_debug_SUITE.erl
index 87778dd0c2..e5c904cfb9 100644
--- a/erts/emulator/test/erts_debug_SUITE.erl
+++ b/erts/emulator/test/erts_debug_SUITE.erl
@@ -67,6 +67,9 @@ test_size(Config) when is_list(Config) ->
     2 = do_test_size({[]}),
     3 = do_test_size({a,b}),
     7 = do_test_size({a,[b,c]}),
+    8 = do_test_size(#{b => 2,c => 3}),
+    4 = do_test_size(#{}),
+    32 = do_test_size(#{b => 2,c => 3,txt => "hello world"}),
 
     %% Test internal consistency of sizes, but without testing
     %% exact sizes.
@@ -97,6 +100,9 @@ test_size(Config) when is_list(Config) ->
     do_test_size({SimplestFun,SimplestFun},
 		 2*FunSz0+do_test_size({a,b}),
 		 FunSz0+do_test_size({a,b})),
+
+    M = id(#{ "atom" => first, i => 0}),
+    do_test_size([M,M#{ "atom" := other },M#{i := 42}],54,32),
     ok.
 
 do_test_size(Term) ->