diff --git a/piclib/built-in.scm b/piclib/built-in.scm
index 3f6eb5a7..c57aef21 100644
--- a/piclib/built-in.scm
+++ b/piclib/built-in.scm
@@ -777,14 +777,20 @@
   (apply vector list))
 
 (define (vector-copy! to at from . opts)
-  (let ((start (if (pair? opts) (car opts) 0))
-	(end (if (>= (length opts) 2)
-		 (cadr opts)
-		 (vector-length from))))
-    (do ((i at (+ i 1))
-	 (j start (+ j 1)))
-	((= j end))
-      (vector-set! to i (vector-ref from j)))))
+  (let* ((start (if (pair? opts) (car opts) 0))
+         (end (if (>= (length opts) 2)
+                  (cadr opts)
+                  (vector-length from)))
+         (vs #f))
+    (if (eq? from to)
+        (begin
+          (set! vs (make-vector (- end start)))
+          (vector-copy! vs 0 from start end)
+          (vector-copy! to at vs))
+        (do ((i at (+ i 1))
+             (j start (+ j 1)))
+            ((= j end))
+          (vector-set! to i (vector-ref from j))))))
 
 (define (vector-copy v . opts)
   (let ((start (if (pair? opts) (car opts) 0))
@@ -836,14 +842,20 @@
 	(bytevector-u8-set! v i (car l))))))
 
 (define (bytevector-copy! to at from . opts)
-  (let ((start (if (pair? opts) (car opts) 0))
-	(end (if (>= (length opts) 2)
+  (let* ((start (if (pair? opts) (car opts) 0))
+         (end (if (>= (length opts) 2)
 		 (cadr opts)
-		 (bytevector-length from))))
-    (do ((i at (+ i 1))
-	 (j start (+ j 1)))
-	((= j end))
-      (bytevector-u8-set! to i (bytevector-u8-ref from j)))))
+		 (bytevector-length from)))
+         (vs #f))
+    (if (eq? from to)
+        (begin
+          (set! vs (make-bytevector (- end start)))
+          (bytevector-copy! vs 0 from start end)
+          (bytevector-copy! to at vs))
+        (do ((i at (+ i 1))
+             (j start (+ j 1)))
+            ((= j end))
+          (bytevector-u8-set! to i (bytevector-u8-ref from j))))))
 
 (define (bytevector-copy v . opts)
   (let ((start (if (pair? opts) (car opts) 0))