diff --git a/engine.c b/engine.c
index b4940e9c91..f7429b8655 100644
--- a/engine.c
+++ b/engine.c
@@ -372,7 +372,7 @@ int32 CmdRenameEngine(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 {
 	StringID str;
 
-	if (!IsEngineIndex(p1) || _cmd_text[0] == '\0') return CMD_ERROR;
+	if (!IsEngineIndex(p1) || _cmd_text == NULL || _cmd_text[0] == '\0') return CMD_ERROR;
 
 	str = AllocateNameUnique(_cmd_text, 0);
 	if (str == 0) return CMD_ERROR;
diff --git a/misc_cmd.c b/misc_cmd.c
index 4293706ba0..5f2dde6849 100644
--- a/misc_cmd.c
+++ b/misc_cmd.c
@@ -187,7 +187,7 @@ int32 CmdChangeCompanyName(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	StringID str;
 	Player *p;
 
-	if (_cmd_text[0] == '\0') return CMD_ERROR;
+	if (_cmd_text == NULL || _cmd_text[0] == '\0') return CMD_ERROR;
 
 	str = AllocateNameUnique(_cmd_text, 4);
 	if (str == 0) return CMD_ERROR;
diff --git a/signs.c b/signs.c
index 4b2d48cd12..3e553e4da9 100644
--- a/signs.c
+++ b/signs.c
@@ -151,7 +151,7 @@ int32 CmdRenameSign(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 
 	/* If _cmd_text 0 means the new text for the sign is non-empty.
 	 * So rename the sign. If it is empty, it has no name, so delete it */
-	if (_cmd_text[0] != '\0') {
+	if (_cmd_text != NULL && _cmd_text[0] != '\0') {
 		/* Create the name */
 		StringID str = AllocateName(_cmd_text, 0);
 		if (str == 0) return CMD_ERROR;
diff --git a/station_cmd.c b/station_cmd.c
index c9f06fb17d..5b7f206205 100644
--- a/station_cmd.c
+++ b/station_cmd.c
@@ -2645,7 +2645,7 @@ int32 CmdRenameStation(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	StringID str;
 	Station *st;
 
-	if (!IsValidStationID(p1) || _cmd_text[0] == '\0') return CMD_ERROR;
+	if (!IsValidStationID(p1) || _cmd_text == NULL || _cmd_text[0] == '\0') return CMD_ERROR;
 	st = GetStation(p1);
 
 	if (!CheckOwnership(st->owner)) return CMD_ERROR;
diff --git a/town_cmd.c b/town_cmd.c
index 6e9a92d1fb..d75c7f0128 100644
--- a/town_cmd.c
+++ b/town_cmd.c
@@ -1373,7 +1373,7 @@ int32 CmdRenameTown(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	StringID str;
 	Town *t;
 
-	if (!IsValidTownID(p1) || _cmd_text[0] == '\0') return CMD_ERROR;
+	if (!IsValidTownID(p1) || _cmd_text == NULL || _cmd_text[0] == '\0') return CMD_ERROR;
 
 	t = GetTown(p1);
 
diff --git a/vehicle.c b/vehicle.c
index 6190a610c4..cca8c6a0d3 100644
--- a/vehicle.c
+++ b/vehicle.c
@@ -2633,7 +2633,7 @@ int32 CmdNameVehicle(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	Vehicle *v;
 	StringID str;
 
-	if (!IsValidVehicleID(p1) || _cmd_text[0] == '\0') return CMD_ERROR;
+	if (!IsValidVehicleID(p1) || _cmd_text == NULL || _cmd_text[0] == '\0') return CMD_ERROR;
 
 	v = GetVehicle(p1);
 
diff --git a/waypoint.c b/waypoint.c
index 7c05a9bd3a..5de5724208 100644
--- a/waypoint.c
+++ b/waypoint.c
@@ -319,7 +319,7 @@ int32 CmdRenameWaypoint(TileIndex tile, uint32 flags, uint32 p1, uint32 p2)
 	wp = GetWaypoint(p1);
 	if (!CheckTileOwnership(wp->xy)) return CMD_ERROR;
 
-	if (_cmd_text[0] != '\0') {
+	if (_cmd_text != NULL && _cmd_text[0] != '\0') {
 		StringID str = AllocateNameUnique(_cmd_text, 0);
 
 		if (str == 0) return CMD_ERROR;