diff --git a/src/port/win32setlocale.c b/src/port/win32setlocale.c
index cbf109836b..278d836b4d 100644
--- a/src/port/win32setlocale.c
+++ b/src/port/win32setlocale.c
@@ -164,19 +164,33 @@ map_locale(const struct locale_map * map, const char *locale)
 	return locale;
 }
 
+static CRITICAL_SECTION setlocale_cs;
+static INIT_ONCE init_once;
+static BOOL CALLBACK init_setlocale_cs(PINIT_ONCE pInitOnce, PVOID pParam, PVOID pCtx)
+{
+	InitializeCriticalSection((PCRITICAL_SECTION)pParam);
+	return TRUE;
+}
+
 char *
 pgwin32_setlocale(int category, const char *locale)
 {
 	const char *argument;
 	char	   *result;
 
+	if (InitOnceExecuteOnce(&init_once, init_setlocale_cs, (PVOID)&setlocale_cs, NULL) == 0) {
+		abort();
+	}
+
 	if (locale == NULL)
 		argument = NULL;
 	else
 		argument = map_locale(locale_map_argument, locale);
 
 	/* Call the real setlocale() function */
+	EnterCriticalSection(&setlocale_cs);
 	result = setlocale(category, argument);
+	LeaveCriticalSection(&setlocale_cs);
 
 	/*
 	 * setlocale() is specified to return a "char *" that the caller is