see https://github.com/moonjit/moonjit/issues/86

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
---
 src/lib_string.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/lib_string.c b/src/lib_string.c
index 5e2891a9e..a90e189ba 100644
--- a/src/lib_string.c
+++ b/src/lib_string.c
@@ -621,7 +621,7 @@ LJLIB_CF(string_gsub)
   const char *p = luaL_checklstring(L, 2, &lp);
   int  tr = lua_type(L, 3);
   int max_s = luaL_optint(L, 4, (int)(srcl+1));
-  int anchor = (*p == '^') ? (p++, 1) : 0;
+  int anchor = (*p == '^');
   int n = 0;
   MatchState ms;
   luaL_Buffer b;
@@ -629,6 +629,9 @@ LJLIB_CF(string_gsub)
 	tr == LUA_TFUNCTION || tr == LUA_TTABLE))
     lj_err_arg(L, 3, LJ_ERR_NOSFT);
   luaL_buffinit(L, &b);
+  if (anchor) {
+    p++; lp--;  /* skip anchor character */
+  }
   ms.L = L;
   ms.src_init = src;
   ms.src_end = src+srcl;