diff --git a/lib/command.c b/lib/command.c
index 168fe56..0e61e0d 100644
--- a/lib/command.c
+++ b/lib/command.c
@@ -78,7 +78,7 @@
 /* Utility function to concatenate argv argument into a single string
    with inserting ' ' character between each argument.  */
 char *
-argv_concat (char **argv, int argc, int shift)
+argv_concat (const char **argv, int argc, int shift)
 {
   int i;
   int len;