diff --git a/src/Makefile.dep b/src/Makefile.dep
index 484553c4..82834811 100644
--- a/src/Makefile.dep
+++ b/src/Makefile.dep
@@ -28,7 +28,8 @@ lib_jit.o: lib_jit.c lua.h luaconf.h lauxlib.h lualib.h lj_arch.h \
 lib_math.o: lib_math.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
  lj_def.h lj_arch.h lj_lib.h lj_vm.h lj_libdef.h
 lib_os.o: lib_os.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h lj_def.h \
- lj_arch.h lj_err.h lj_errmsg.h lj_lib.h lj_libdef.h
+ lj_arch.h lj_gc.h lj_err.h lj_errmsg.h lj_buf.h lj_str.h lj_lib.h \
+ lj_libdef.h
 lib_package.o: lib_package.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
  lj_def.h lj_arch.h lj_err.h lj_errmsg.h lj_lib.h
 lib_string.o: lib_string.c lua.h luaconf.h lauxlib.h lualib.h lj_obj.h \
diff --git a/src/lib_os.c b/src/lib_os.c
index 0a784129..d0291f52 100644
--- a/src/lib_os.c
+++ b/src/lib_os.c
@@ -18,7 +18,9 @@
 #include "lualib.h"
 
 #include "lj_obj.h"
+#include "lj_gc.h"
 #include "lj_err.h"
+#include "lj_buf.h"
 #include "lj_lib.h"
 
 #if LJ_TARGET_POSIX
@@ -197,23 +199,25 @@ LJLIB_CF(os_date)
     setfield(L, "wday", stm->tm_wday+1);
     setfield(L, "yday", stm->tm_yday+1);
     setboolfield(L, "isdst", stm->tm_isdst);
-  } else {
-    char cc[3];
-    luaL_Buffer b;
-    cc[0] = '%'; cc[2] = '\0';
-    luaL_buffinit(L, &b);
-    for (; *s; s++) {
-      if (*s != '%' || *(s + 1) == '\0') {  /* No conversion specifier? */
-	luaL_addchar(&b, *s);
-      } else {
-	size_t reslen;
-	char buff[200];  /* Should be big enough for any conversion result. */
-	cc[1] = *(++s);
-	reslen = strftime(buff, sizeof(buff), cc, stm);
-	luaL_addlstring(&b, buff, reslen);
+  } else if (*s) {
+    SBuf *sb = &G(L)->tmpbuf;
+    MSize sz = 0;
+    const char *q;
+    for (q = s; *q; q++)
+      sz += (*q == '%') ? 30 : 1;  /* Overflow doesn't matter. */
+    setmref(sb->L, L);
+    for (;;) {
+      char *buf = lj_buf_need(sb, sz);
+      size_t len = strftime(buf, sbufsz(sb), s, stm);
+      if (len) {
+	setstrV(L, L->top-1, lj_str_new(L, buf, len));
+	lj_gc_check(L);
+	break;
       }
+      sz += (sz|1);
     }
-    luaL_pushresult(&b);
+  } else {
+    setstrV(L, L->top-1, &G(L)->strempty);
   }
   return 1;
 }