diff --git a/libs/ardour/ardour/chan_mapping.h b/libs/ardour/ardour/chan_mapping.h
index 7a4d41123e..21838a1221 100644
--- a/libs/ardour/ardour/chan_mapping.h
+++ b/libs/ardour/ardour/chan_mapping.h
@@ -104,7 +104,10 @@ public:
 	 */
 	bool     is_subset (const ChanMapping& superset) const;
 
-#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#if defined(_MSC_VER) /* && (_MSC_VER < 1900)
+	                   * Regarding the note (below) it was initially
+	                   * thought that this got fixed in VS2015 - but
+	                   * in fact it's still faulty (JE - Feb 2021) */
 	/* Use the older (heap based) mapping for early versions of MSVC.
 	 * In fact it might be safer to use this for all MSVC builds - as
 	 * our StackAllocator class depends on 'boost::aligned_storage'
diff --git a/libs/ardour/ardour/plugin_insert.h b/libs/ardour/ardour/plugin_insert.h
index f15967640b..097c8e80ce 100644
--- a/libs/ardour/ardour/plugin_insert.h
+++ b/libs/ardour/ardour/plugin_insert.h
@@ -371,7 +371,10 @@ private:
 	/* ordered map [plugin instance ID] => ARDOUR::ChanMapping
 	 * TODO: consider replacing with boost::flat_map<> or std::vector<>.
 	 */
-#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#if defined(_MSC_VER) /* && (_MSC_VER < 1900)
+	                   * Regarding the note (below) it was initially
+	                   * thought that this got fixed in VS2015 - but
+	                   * in fact it's still faulty (JE - Feb 2021) */
 	/* Use the older (heap based) mapping for early versions of MSVC.
 	 * In fact it might be safer to use this for all MSVC builds - as
 	 * our StackAllocator class depends on 'boost::aligned_storage'