diff --git a/target-arm/arm-semi.c b/target-arm/arm-semi.c
index 74a67e9fdd..a2a7369567 100644
--- a/target-arm/arm-semi.c
+++ b/target-arm/arm-semi.c
@@ -436,12 +436,19 @@ uint32_t do_arm_semihosting(CPUARMState *env)
             size_t input_size;
             size_t output_size;
             int status = 0;
+#if !defined(CONFIG_USER_ONLY)
+            const char *cmdline;
+#endif
             GET_ARG(0);
             GET_ARG(1);
             input_size = arg1;
             /* Compute the size of the output string.  */
 #if !defined(CONFIG_USER_ONLY)
-            output_size = strlen(semihosting_get_cmdline()) + 1;
+            cmdline = semihosting_get_cmdline();
+            if (cmdline == NULL) {
+                cmdline = ""; /* Default to an empty line. */
+            }
+            output_size = strlen(cmdline) + 1; /* Count terminating 0. */
 #else
             unsigned int i;
 
@@ -472,7 +479,7 @@ uint32_t do_arm_semihosting(CPUARMState *env)
 
             /* Copy the command-line arguments.  */
 #if !defined(CONFIG_USER_ONLY)
-            pstrcpy(output_buffer, output_size, semihosting_get_cmdline());
+            pstrcpy(output_buffer, output_size, cmdline);
 #else
             if (output_size == 1) {
                 /* Empty command-line.  */