diff --git a/src/c/main.d b/src/c/main.d
index 362334b64..f5cd8a2cc 100644
--- a/src/c/main.d
+++ b/src/c/main.d
@@ -83,8 +83,8 @@ static cl_fixnum option_values[ECL_OPT_LIMIT+1] = {
 	128,		/* ECL_OPT_FRAME_STACK_SAFETY_AREA */
 	32768,		/* ECL_OPT_LISP_STACK_SIZE */
 	128,		/* ECL_OPT_LISP_STACK_SAFETY_AREA */
-	512*1024,	/* ECL_OPT_C_STACK_SIZE */
-	16*1024,	/* ECL_OPT_C_STACK_SAFETY_AREA */
+	128*sizeof(cl_index)*1024, /* ECL_OPT_C_STACK_SIZE */
+	4*sizeof(cl_index)*1024, /* ECL_OPT_C_STACK_SAFETY_AREA */
 	1,		/* ECL_OPT_SIGALTSTACK_SIZE */
 #if ECL_FIXNUM_BITS <= 32
 	1024*1024*1024, /* ECL_OPT_HEAP_SIZE */