diff --git a/src/buildvm_lib.c b/src/buildvm_lib.c
index e77240c5..c98d6312 100644
--- a/src/buildvm_lib.c
+++ b/src/buildvm_lib.c
@@ -23,7 +23,7 @@ enum {
   REGFUNC_NOREGUV
 };
 
-static void libdef_name(char *p, int kind)
+static void libdef_name(const char *p, int kind)
 {
   size_t n = strlen(p);
   if (kind != LIBINIT_STRING) {