diff --git a/libs/pbd/debug.cc b/libs/pbd/debug.cc
index e6d4abcee7..0940146aef 100644
--- a/libs/pbd/debug.cc
+++ b/libs/pbd/debug.cc
@@ -56,6 +56,7 @@ DebugBits PBD::DEBUG::Configuration = PBD::new_debug_bit ("configuration");
 DebugBits PBD::DEBUG::UndoHistory = PBD::new_debug_bit ("undohistory");
 DebugBits PBD::DEBUG::Timing = PBD::new_debug_bit ("timing");
 DebugBits PBD::DEBUG::Threads = PBD::new_debug_bit ("threads");
+DebugBits PBD::DEBUG::Locale = PBD::new_debug_bit ("locale");
 
 /* These are debug bits that are used by backends. Since these are loaded dynamically,
    after command-line parsing, defining them in code that is part of the backend
diff --git a/libs/pbd/locale_guard.cc b/libs/pbd/locale_guard.cc
index 6e95ea9dcd..b4225d3875 100644
--- a/libs/pbd/locale_guard.cc
+++ b/libs/pbd/locale_guard.cc
@@ -22,8 +22,10 @@
 #include <assert.h>
 #include <locale.h>
 
-#include "pbd/locale_guard.h"
+#include "pbd/compose.h"
+#include "pbd/debug.h"
 #include "pbd/error.h"
+#include "pbd/locale_guard.h"
 
 using namespace PBD;
 
@@ -39,17 +41,17 @@ LocaleGuard::LocaleGuard ()
 {
 	char* actual = setlocale (LC_NUMERIC, NULL);
 	if (strcmp ("C", actual)) {
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: change locale from '%1' to 'C'\n", actual));
 		/* purpose of LocaleGuard is to make sure we're using "C" for
 		   the numeric locale during its lifetime, so make it so.
 		*/
 		old_c = strdup (actual);
-		/* this changes both C++ and C locale (according to specs) */
+		/* this changes both C++ and C locale */
 		std::locale::global (std::locale (std::locale::classic(), "C", std::locale::numeric));
-		/* ..but maybe not.. */
-		setlocale (LC_NUMERIC, "C");
 	}
 	if (old_cpp != std::locale::classic ()) {
 		PBD::error << "LocaleGuard: initial C++ locale is not 'C'. Expect non-portable session files.\n";
+		DEBUG_TRACE (DEBUG::Locale, "LG: initial C++ locale is not 'C'. Expect non-portable session files.\n");
 	}
 }
 
@@ -67,11 +69,14 @@ LocaleGuard::~LocaleGuard ()
 		 */
 		if (old_cpp != std::locale::classic ()) {
 			PBD::error << "LocaleGuard: someone (a plugin) changed the C++ locale, expect non-portable session files.\n";
+			DEBUG_TRACE (DEBUG::Locale, "LG: someone (a plugin) changed the C++ locale, expect non-portable session files.\n");
 		}
 		std::locale::global (old_cpp);
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: restore C++ locale: '%1'\n", old_cpp.name ()));
 	}
 	if (old_c && strcmp (old_c, actual)) {
 		setlocale (LC_NUMERIC, old_c);
+		DEBUG_TRACE (DEBUG::Locale, string_compose ("LG: restore C locale: '%1'\n", old_c));
 	}
 	free (old_c);
 }
diff --git a/libs/pbd/pbd/debug.h b/libs/pbd/pbd/debug.h
index 3696e7a346..8db198e82e 100644
--- a/libs/pbd/pbd/debug.h
+++ b/libs/pbd/pbd/debug.h
@@ -58,6 +58,7 @@ namespace PBD {
 		LIBPBD_API extern DebugBits UndoHistory;
 		LIBPBD_API extern DebugBits Timing;
 		LIBPBD_API extern DebugBits Threads;
+		LIBPBD_API extern DebugBits Locale;
 
 		/* See notes in ../debug.cc on why these are defined here */