diff --git a/lib/mnesia/src/mnesia_frag_hash.erl b/lib/mnesia/src/mnesia_frag_hash.erl
index 610ba2535c28..d70579c3b3c2 100644
--- a/lib/mnesia/src/mnesia_frag_hash.erl
+++ b/lib/mnesia/src/mnesia_frag_hash.erl
@@ -101,21 +101,19 @@ del_frag(OldState) ->
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-key_to_frag_number(#hash_state{function = phash, next_n_to_split = SplitN, n_doubles = L}, Key) ->
-    P = SplitN,
-    A = erlang:phash(Key, power2(L)),
+key_to_frag_number(#hash_state{function = phash, n_fragments = N, n_doubles = L}, Key) ->
+    A = erlang:phash(Key, power2(L + 1)),
     if
-	A < P ->
-	    erlang:phash(Key, power2(L + 1));
+	A > N ->
+	    A - power2(L);
 	true ->
 	    A
     end;
-key_to_frag_number(#hash_state{function = phash2, next_n_to_split = SplitN, n_doubles = L}, Key) ->
-    P = SplitN,
-    A = erlang:phash2(Key, power2(L)) + 1,
+key_to_frag_number(#hash_state{function = phash2, n_fragments = N, n_doubles = L}, Key) ->
+    A = erlang:phash2(Key, power2(L + 1)) + 1,
     if
-	A < P ->
-	    erlang:phash2(Key, power2(L + 1)) + 1;
+	A > N ->
+	    A - power2(L);
 	true ->
 	    A
     end;
diff --git a/lib/mnesia/test/mnesia_frag_hash_test.erl b/lib/mnesia/test/mnesia_frag_hash_test.erl
new file mode 100644
index 000000000000..095d25e74f7a
--- /dev/null
+++ b/lib/mnesia/test/mnesia_frag_hash_test.erl
@@ -0,0 +1,94 @@
+-module(mnesia_frag_hash_test).
+
+-export([test/0]).
+
+-define(NUM_FRAGS, 20).
+-define(NUM_KEYS, 10000).
+
+-record(hash_state,
+	{n_fragments,
+	 next_n_to_split,
+	 n_doubles,
+	 function}).
+
+% OLD mnesia_frag_hash:key_to_frag_number/2.
+old_key_to_frag_number(#hash_state{function = phash, next_n_to_split = SplitN, n_doubles = L}, Key) ->
+    P = SplitN,
+    A = erlang:phash(Key, power2(L)),
+    if
+	A < P ->
+	    erlang:phash(Key, power2(L + 1));
+	true ->
+	    A
+    end;
+old_key_to_frag_number(#hash_state{function = phash2, next_n_to_split = SplitN, n_doubles = L}, Key) ->
+    P = SplitN,
+    A = erlang:phash2(Key, power2(L)) + 1,
+    if
+	A < P ->
+	    erlang:phash2(Key, power2(L + 1)) + 1;
+	true ->
+	    A
+    end;
+old_key_to_frag_number(OldState, Key) ->
+    State = convert_old_state(OldState),
+    old_key_to_frag_number(State, Key).
+
+
+% NEW mnesia_frag_hash:key_to_frag_number/2.
+new_key_to_frag_number(#hash_state{function = phash, n_fragments = N, n_doubles = L}, Key) ->
+    A = erlang:phash(Key, power2(L + 1)),
+    if
+	A > N ->
+	    A - power2(L);
+	true ->
+	    A
+    end;
+new_key_to_frag_number(#hash_state{function = phash2, n_fragments = N, n_doubles = L}, Key) ->
+    A = erlang:phash2(Key, power2(L + 1)) + 1,
+    if
+	A > N ->
+	    A - power2(L);
+	true ->
+	    A
+    end;
+new_key_to_frag_number(OldState, Key) ->
+    State = convert_old_state(OldState),
+    new_key_to_frag_number(State, Key).
+
+
+% Helpers for key_to_frag_number functions.
+
+power2(Y) ->
+    1 bsl Y. % trunc(math:pow(2, Y)).
+
+convert_old_state({hash_state, N, P, L}) ->
+    #hash_state{n_fragments     = N,
+		next_n_to_split = P,
+		n_doubles       = L,
+		function        = phash}.
+
+
+test() ->
+    test2(mnesia_frag_hash:init_state(undefined, undefined)), % phash2
+    test2({hash_state, 1, 1, 0}). % phash
+
+test2(I) ->
+    test_keys(I),
+    lists:foldl(
+        fun(_, S) -> test_frag(S) end,
+        I, lists:seq(1, ?NUM_FRAGS)),
+    ok.
+
+test_frag(State) ->
+    {State2,_,_} = mnesia_frag_hash:add_frag(State),
+    test_keys(State2),
+    State2.
+
+test_keys(State) ->
+    [test_key(State, Key) || Key <- lists:seq(1, ?NUM_KEYS)].
+
+test_key(State, Key) ->
+    Old = old_key_to_frag_number(State, Key),
+    New = new_key_to_frag_number(State, Key),
+    Old = New.