diff --git a/deps/lua/src/llex.c b/deps/lua/src/llex.c
index 88c6790c0..efad70922 100644
--- a/deps/lua/src/llex.c
+++ b/deps/lua/src/llex.c
@@ -138,6 +138,7 @@ static void inclinenumber (LexState *ls) {
 
 
 void luaX_setinput (lua_State *L, LexState *ls, ZIO *z, TString *source) {
+  ls->t.token = 0;
   ls->decpoint = '.';
   ls->L = L;
   ls->lookahead.token = TK_EOS;  /* no look-ahead token */
@@ -206,9 +207,13 @@ static void read_numeral (LexState *ls, SemInfo *seminfo) {
     trydecpoint(ls, seminfo); /* try to update decimal point separator */
 }
 
-
-static int skip_sep (LexState *ls) {
-  int count = 0;
+/*
+** reads a sequence '[=*[' or ']=*]', leaving the last bracket.
+** If a sequence is well-formed, return its number of '='s + 2; otherwise,
+** return 1 if there is no '='s or 0 otherwise (an unfinished '[==...').
+*/
+static size_t skip_sep (LexState *ls) {
+  size_t count = 0;
   int s = ls->current;
   lua_assert(s == '[' || s == ']');
   save_and_next(ls);
@@ -216,11 +221,13 @@ static int skip_sep (LexState *ls) {
     save_and_next(ls);
     count++;
   }
-  return (ls->current == s) ? count : (-count) - 1;
+   return (ls->current == s) ? count + 2
+          : (count == 0) ? 1
+          : 0;
 }
 
 
-static void read_long_string (LexState *ls, SemInfo *seminfo, int sep) {
+static void read_long_string (LexState *ls, SemInfo *seminfo, size_t sep) {
   int cont = 0;
   (void)(cont);  /* avoid warnings when `cont' is not used */
   save_and_next(ls);  /* skip 2nd `[' */
@@ -270,8 +277,8 @@ static void read_long_string (LexState *ls, SemInfo *seminfo, int sep) {
     }
   } endloop:
   if (seminfo)
-    seminfo->ts = luaX_newstring(ls, luaZ_buffer(ls->buff) + (2 + sep),
-                                     luaZ_bufflen(ls->buff) - 2*(2 + sep));
+    seminfo->ts = luaX_newstring(ls, luaZ_buffer(ls->buff) + sep,
+                                     luaZ_bufflen(ls->buff) - 2 * sep);
 }
 
 
@@ -346,9 +353,9 @@ static int llex (LexState *ls, SemInfo *seminfo) {
         /* else is a comment */
         next(ls);
         if (ls->current == '[') {
-          int sep = skip_sep(ls);
+          size_t sep = skip_sep(ls);
           luaZ_resetbuffer(ls->buff);  /* `skip_sep' may dirty the buffer */
-          if (sep >= 0) {
+          if (sep >= 2) {
             read_long_string(ls, NULL, sep);  /* long comment */
             luaZ_resetbuffer(ls->buff);
             continue;
@@ -360,13 +367,14 @@ static int llex (LexState *ls, SemInfo *seminfo) {
         continue;
       }
       case '[': {
-        int sep = skip_sep(ls);
-        if (sep >= 0) {
+        size_t sep = skip_sep(ls);
+        if (sep >= 2) {
           read_long_string(ls, seminfo, sep);
           return TK_STRING;
         }
-        else if (sep == -1) return '[';
-        else luaX_lexerror(ls, "invalid long string delimiter", TK_STRING);
+        else if (sep == 0)  /* '[=...' missing second bracket */
+          luaX_lexerror(ls, "invalid long string delimiter", TK_STRING);
+        return '[';
       }
       case '=': {
         next(ls);
diff --git a/tests/unit/scripting.tcl b/tests/unit/scripting.tcl
index 9e446a394..65b0ac723 100644
--- a/tests/unit/scripting.tcl
+++ b/tests/unit/scripting.tcl
@@ -355,13 +355,6 @@ start_server {tags {"scripting"}} {
         set e
     } {*against a key*}
 
-    test {EVAL - JSON string encoding a string larger than 2GB} {
-        run_script {
-            local s = string.rep("a", 1024 * 1024 * 1024)
-            return #cjson.encode(s..s..s)
-        } 0
-    } {3221225474} {large-memory} ;# length includes two double quotes at both ends
-
     test {EVAL - JSON numeric decoding} {
         # We must return the table as a string because otherwise
         # Redis converts floats to ints and we get 0 and 1023 instead
@@ -1207,6 +1200,52 @@ start_server {tags {"scripting"}} {
     } {*Script attempted to access nonexistent global variable 'print'*}
 }
 
+# start a new server to test the large-memory tests
+start_server {tags {"scripting external:skip large-memory"}} {
+    test {EVAL - JSON string encoding a string larger than 2GB} {
+        run_script {
+            local s = string.rep("a", 1024 * 1024 * 1024)
+            return #cjson.encode(s..s..s)
+        } 0
+    } {3221225474} ;# length includes two double quotes at both ends
+
+    test {EVAL - Test long escape sequences for strings} {
+        run_script {
+            -- Generate 1gb '==...==' separator
+            local s = string.rep('=', 1024 * 1024)
+            local t = {} for i=1,1024 do t[i] = s end
+            local sep = table.concat(t)
+            collectgarbage('collect')
+
+            local code = table.concat({'return [',sep,'[x]',sep,']'})
+            collectgarbage('collect')
+
+            -- Load the code and run it. Script will return the string length.
+            -- Escape sequence: [=....=[ to ]=...=] will be ignored
+            -- Actual string is a single character: 'x'. Script will return 1
+            local func = loadstring(code)
+            return #func()
+        } 0
+    } {1}
+
+    test {EVAL - Lua can parse string with too many new lines} {
+        # Create a long string consisting only of newline characters. When Lua
+        # fails to parse a string, it typically includes a snippet like
+        # "... near ..." in the error message to indicate the last recognizable
+        # token. In this test, since the input contains only newlines, there
+        # should be no identifiable token, so the error message should contain
+        # only the actual error, without a near clause.
+
+        run_script {
+           local s = string.rep('\n', 1024 * 1024)
+           local t = {} for i=1,2048 do t[#t+1] = s end
+           local lines = table.concat(t)
+           local fn, err = loadstring(lines)
+           return err
+        } 0
+    } {*chunk has too many lines}
+}
+
 # Start a new server to test lua-enable-deprecated-api config
 foreach enabled {no yes} {
 start_server [subst {tags {"scripting external:skip"} overrides {lua-enable-deprecated-api $enabled}}] {