diff --git a/blackbox.c b/blackbox.c
index 7c84a16..2ec8693 100644
--- a/blackbox.c
+++ b/blackbox.c
@@ -511,7 +511,8 @@ static char *encode_ui(const game_ui *ui)
     return dupstr(buf);
 }
 
-static void decode_ui(game_ui *ui, const char *encoding)
+static void decode_ui(game_ui *ui, const char *encoding,
+                      const game_state *state)
 {
     sscanf(encoding, "E%d", &ui->errors);
 }
diff --git a/devel.but b/devel.but
index 9ce8eee..ae0a84d 100644
--- a/devel.but
+++ b/devel.but
@@ -890,14 +890,17 @@ this function it can just set the pointer to \cw{NULL}.
 
 \S{backend-decode-ui} \cw{decode_ui()}
 
-\c void (*decode_ui)(game_ui *ui, const char *encoding);
+\c void (*decode_ui)(game_ui *ui, const char *encoding,
+\c                   const game_state *state);
 
 This function parses a string previously output by \cw{encode_ui()},
 and writes the decoded data back into the freshly-created \c{game_ui}
 structure provided.  If the string is invalid, the function should do
 the best it can, which might just mean not changing the \c{game_ui}
 structure at all.  This might happen if a save file is corrupted, or
-simply from a newer version that encodes more \c{game_ui} data.
+simply from a newer version that encodes more \c{game_ui} data.  The
+current \c{game_state} is provided in case the function needs to
+refer to it for validation.
 
 Like \cw{encode_ui()}, \cw{decode_ui()} is optional.  If a back-end
 doesn't need this function it can just set the pointer to \cw{NULL}.
diff --git a/guess.c b/guess.c
index 1dbea4c..dc02d57 100644
--- a/guess.c
+++ b/guess.c
@@ -452,7 +452,8 @@ static char *encode_ui(const game_ui *ui)
     return sresize(ret, p - ret, char);
 }
 
-static void decode_ui(game_ui *ui, const char *encoding)
+static void decode_ui(game_ui *ui, const char *encoding,
+                      const game_state *state)
 {
     int i;
     const char *p = encoding;
diff --git a/inertia.c b/inertia.c
index 42c2f5b..a352514 100644
--- a/inertia.c
+++ b/inertia.c
@@ -1527,7 +1527,8 @@ static char *encode_ui(const game_ui *ui)
     return dupstr(buf);
 }
 
-static void decode_ui(game_ui *ui, const char *encoding)
+static void decode_ui(game_ui *ui, const char *encoding,
+                      const game_state *state)
 {
     int p = 0;
     sscanf(encoding, "D%d%n", &ui->deaths, &p);
diff --git a/midend.c b/midend.c
index 2e49e8d..c9ef415 100644
--- a/midend.c
+++ b/midend.c
@@ -2542,7 +2542,8 @@ static const char *midend_deserialise_internal(
 
     data.ui = me->ourgame->new_ui(data.states[0].state);
     if (data.uistr && me->ourgame->decode_ui)
-        me->ourgame->decode_ui(data.ui, data.uistr);
+        me->ourgame->decode_ui(data.ui, data.uistr,
+                               data.states[data.statepos-1].state);
 
     /*
      * Run the externally provided check function, and abort if it
diff --git a/mines.c b/mines.c
index e9437cb..c9deb82 100644
--- a/mines.c
+++ b/mines.c
@@ -2413,7 +2413,8 @@ static char *encode_ui(const game_ui *ui)
     return dupstr(buf);
 }
 
-static void decode_ui(game_ui *ui, const char *encoding)
+static void decode_ui(game_ui *ui, const char *encoding,
+                      const game_state *state)
 {
     int p= 0;
     sscanf(encoding, "D%d%n", &ui->deaths, &p);
diff --git a/net.c b/net.c
index 7f90047..d920c5c 100644
--- a/net.c
+++ b/net.c
@@ -2041,7 +2041,8 @@ static char *encode_ui(const game_ui *ui)
     return dupstr(buf);
 }
 
-static void decode_ui(game_ui *ui, const char *encoding)
+static void decode_ui(game_ui *ui, const char *encoding,
+                      const game_state *state)
 {
     sscanf(encoding, "O%d,%d;C%d,%d",
 	   &ui->org_x, &ui->org_y, &ui->cx, &ui->cy);
diff --git a/puzzles.h b/puzzles.h
index 6b5ff6e..27e1443 100644
--- a/puzzles.h
+++ b/puzzles.h
@@ -664,7 +664,8 @@ struct game {
     game_ui *(*new_ui)(const game_state *state);
     void (*free_ui)(game_ui *ui);
     char *(*encode_ui)(const game_ui *ui);
-    void (*decode_ui)(game_ui *ui, const char *encoding);
+    void (*decode_ui)(game_ui *ui, const char *encoding,
+                      const game_state *state);
     key_label *(*request_keys)(const game_params *params, int *nkeys);
     void (*changed_state)(game_ui *ui, const game_state *oldstate,
                           const game_state *newstate);