diff --git a/src/os/unix/unix.cpp b/src/os/unix/unix.cpp
index c27a97a082..8963cb61a0 100644
--- a/src/os/unix/unix.cpp
+++ b/src/os/unix/unix.cpp
@@ -24,6 +24,7 @@
 #include <time.h>
 #include <signal.h>
 #include <pthread.h>
+#include <atomic>
 
 #ifdef WITH_SDL2
 #include <SDL.h>
@@ -160,6 +161,8 @@ static std::string convert_tofrom_fs(iconv_t convd, const std::string &name)
 	return buf;
 }
 
+std::mutex _iconv_convd_mutex;
+
 /**
  * Convert from OpenTTD's encoding to that of the local environment
  * @param name pointer to a valid string that will be converted
@@ -167,17 +170,25 @@ static std::string convert_tofrom_fs(iconv_t convd, const std::string &name)
  */
 std::string OTTD2FS(const std::string &name)
 {
-	static iconv_t convd = (iconv_t)(-1);
-	if (convd == (iconv_t)(-1)) {
-		const char *env = GetLocalCode();
-		convd = iconv_open(env, INTERNALCODE);
-		if (convd == (iconv_t)(-1)) {
+	static std::atomic<iconv_t> convd{(iconv_t)(-1)};
+	iconv_t local_convd = convd.load(std::memory_order_relaxed);
+	if (local_convd == (iconv_t)(-1)) {
+		{
+			std::unique_lock<std::mutex> lock(_iconv_convd_mutex);
+			local_convd = convd.load(); // Load a second time now that the lock is acquired
+			if (local_convd == (iconv_t)(-1)) {
+				const char *env = GetLocalCode();
+				local_convd = iconv_open(env, INTERNALCODE);
+				if (local_convd != (iconv_t)(-1)) convd.store(local_convd);
+			}
+		}
+		if (local_convd == (iconv_t)(-1)) {
 			DEBUG(misc, 0, "[iconv] conversion from codeset '%s' to '%s' unsupported", INTERNALCODE, env);
 			return name;
 		}
 	}
 
-	return convert_tofrom_fs(convd, name);
+	return convert_tofrom_fs(local_convd, name);
 }
 
 /**
@@ -187,17 +198,25 @@ std::string OTTD2FS(const std::string &name)
  */
 std::string FS2OTTD(const std::string &name)
 {
-	static iconv_t convd = (iconv_t)(-1);
-	if (convd == (iconv_t)(-1)) {
-		const char *env = GetLocalCode();
-		convd = iconv_open(INTERNALCODE, env);
-		if (convd == (iconv_t)(-1)) {
+	static std::atomic<iconv_t> convd{(iconv_t)(-1)};
+	iconv_t local_convd = convd.load(std::memory_order_relaxed);
+	if (local_convd == (iconv_t)(-1)) {
+		{
+			std::unique_lock<std::mutex> lock(_iconv_convd_mutex);
+			local_convd = convd.load(); // Load a second time now that the lock is acquired
+			if (local_convd == (iconv_t)(-1)) {
+				const char *env = GetLocalCode();
+				local_convd = iconv_open(INTERNALCODE, env);
+				if (local_convd != (iconv_t)(-1)) convd.store(local_convd);
+			}
+		}
+		if (local_convd == (iconv_t)(-1)) {
 			DEBUG(misc, 0, "[iconv] conversion from codeset '%s' to '%s' unsupported", env, INTERNALCODE);
 			return name;
 		}
 	}
 
-	return convert_tofrom_fs(convd, name);
+	return convert_tofrom_fs(local_convd, name);
 }
 
 #endif /* WITH_ICONV */