diff --git a/library/ecp.c b/library/ecp.c
index 2a6045f..f14b0b4 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1296,7 +1296,7 @@
     ecp_point R;
     mpi m;
     unsigned long add_c_prev, dbl_c_prev;
-    char *exponents[] =
+    const char *exponents[] =
     {
         "000000000000000000000000000000000000000000000000", /* zero */
         "000000000000000000000000000000000000000000000001", /* one */