diff --git a/libguile/rdelim.c b/libguile/rdelim.c
index 15fd0eea3..8b6d05526 100644
--- a/libguile/rdelim.c
+++ b/libguile/rdelim.c
@@ -225,7 +225,7 @@ SCM_DEFINE (scm_read_line, "%read-line", 0, 1, 0,
 {
   scm_t_port *pt;
   char *s;
-  size_t slen;
+  size_t slen = 0;
   SCM line, term;
 
   if (SCM_UNBNDP (port))