diff --git a/crates/mipsy_web/index.html b/crates/mipsy_web/index.html
index 0f8b07a..9d09be6 100644
--- a/crates/mipsy_web/index.html
+++ b/crates/mipsy_web/index.html
@@ -131,7 +131,11 @@
       }
 
       function set_editor_value(value="") {
-        window.editor.setValue(value);
+        // Don't unnecesarily call editor.setValue(),
+        // since setValue will also reset undo history.
+        if (get_editor_value() !== value) {
+          window.editor.setValue(value);
+        }
       }
 
       function get_editor_value() {