diff --git a/xwords4/wasm/main.c b/xwords4/wasm/main.c
index 4a1b94b0d..d84723297 100644
--- a/xwords4/wasm/main.c
+++ b/xwords4/wasm/main.c
@@ -517,10 +517,10 @@ looper( void* closure )
 }
 
 void
-button( const char* msg )
+button( void* closure, const char* msg )
 {
     XP_Bool draw = XP_FALSE;
-    Globals* globals = sGlobals;
+    Globals* globals = (Globals*)closure;
     BoardCtxt* board = globals->game.board;
     XP_Bool redo;
 
diff --git a/xwords4/wasm/shell_minimal.html b/xwords4/wasm/shell_minimal.html
index 7fb953416..7d283bc90 100644
--- a/xwords4/wasm/shell_minimal.html
+++ b/xwords4/wasm/shell_minimal.html
@@ -195,7 +195,7 @@
 		}
 
         function callButton(name) {
-			Module.ccall('button', null, ['string'], [name]);
+			Module.ccall('button', null, ['number', 'string'], [state.closure, name]);
 		}
 
         function onHaveDevID(closure, devid) {