diff --git a/sim/rx/ChangeLog b/sim/rx/ChangeLog
index f064039582..8d5f1d745e 100644
--- a/sim/rx/ChangeLog
+++ b/sim/rx/ChangeLog
@@ -1,3 +1,7 @@
+2021-02-08  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb-if.c (sim_do_command): Work with a copy of the command.
+
 2021-02-08  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb-if.c (sim_memory_map): New function.
diff --git a/sim/rx/gdb-if.c b/sim/rx/gdb-if.c
index 6f8bfbd1c5..55eb13d12e 100644
--- a/sim/rx/gdb-if.c
+++ b/sim/rx/gdb-if.c
@@ -804,13 +804,13 @@ sim_do_command (SIM_DESC sd, const char *cmd)
     p++;
 
   /* Find the extent of the command word.  */
-  for (p = cmd; *p; p++)
+  for (; *p != '\0'; p++)
     if (isspace (*p))
       break;
 
   /* Null-terminate the command word, and record the start of any
      further arguments.  */
-  if (*p)
+  if (*p != '\0')
     {
       *p = '\0';
       args = p + 1;