diff --git a/src/lib.c b/src/lib.c
index 9ab8b98d..b5450b25 100644
--- a/src/lib.c
+++ b/src/lib.c
@@ -198,8 +198,12 @@ equal2:
 SCM
 last_pair (SCM x)
 {
-  while (x != cell_nil && CDR (x) != cell_nil)
-    x = CDR (x);
+  while (x != cell_nil)
+    {
+      if (CDR (x) == cell_nil)
+        return x;
+      x = CDR (x);
+    }
   return x;
 }