diff --git a/sha1.c b/sha1.c
index 11be704..89b32f4 100644
--- a/sha1.c
+++ b/sha1.c
@@ -258,7 +258,7 @@ sha1_process_bytes (const void *buffer, size_t len, struct sha1_ctx *ctx)
 	{
 	  sha1_process_block (ctx->buffer, 64, ctx);
 	  left_over -= 64;
-	  memcpy (ctx->buffer, &ctx->buffer[16], left_over);
+	  memmove (ctx->buffer, &ctx->buffer[16], left_over);
 	}
       ctx->buflen = left_over;
     }