diff --git a/archival/libarchive/unsafe_prefix.c b/archival/libarchive/unsafe_prefix.c
new file mode 100644
index 0000000..826c673
--- /dev/null
+++ b/archival/libarchive/unsafe_prefix.c
@@ -0,0 +1,36 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+
+#include "libbb.h"
+#include "bb_archive.h"
+
+const char* FAST_FUNC strip_unsafe_prefix(const char *str)
+{
+	const char *cp = str;
+	while (1) {
+		char *cp2;
+		if (*cp == '/') {
+			cp++;
+			continue;
+		}
+		if (strncmp(cp, "/../"+1, 3) == 0) {
+			cp += 3;
+			continue;
+		}
+		cp2 = strstr(cp, "/../");
+		if (!cp2)
+			break;
+		cp = cp2 + 4;
+	}
+	if (cp != str) {
+		static smallint warned = 0;
+		if (!warned) {
+			warned = 1;
+			bb_error_msg("removing leading '%.*s' from member names",
+				(int)(cp - str), str);
+		}
+	}
+	return cp;
+}