diff --git a/lua/nvim-autopairs/conds.lua b/lua/nvim-autopairs/conds.lua
index dc10eeb1..a07518e0 100644
--- a/lua/nvim-autopairs/conds.lua
+++ b/lua/nvim-autopairs/conds.lua
@@ -40,6 +40,7 @@ end
 cond.before_regex = function(regex, length)
     length = length or 1
     if length < 0 then length = nil end
+    length = length and -length
     ---@param opts CondOpts
     return function(opts)
         log.debug('before_regex')
@@ -117,6 +118,7 @@ end
 cond.not_before_regex = function(regex, length)
     length = length or 1
     if length < 0 then length = nil end
+    length = length and -length
     ---@param opts CondOpts
     return function(opts)
         log.debug('not_before_regex')
diff --git a/tests/nvim-autopairs_spec.lua b/tests/nvim-autopairs_spec.lua
index ac2bbe98..ff25a1d3 100644
--- a/tests/nvim-autopairs_spec.lua
+++ b/tests/nvim-autopairs_spec.lua
@@ -8,6 +8,7 @@ local utils = require('nvim-autopairs.utils')
 _G.npairs = npairs;
 
 -- use only = true to test 1 case
+-- stylua: ignore
 local data = {
     {
         -- only = true,
@@ -808,6 +809,17 @@ local data = {
         before   = [[('|') ]],
         after    = [[(''|) ]]
     },
+    {
+        setup_func = function()
+            npairs.add_rules({
+                Rule('123456', '789'):with_pair(cond.before_regex('^12345$', 5)),
+            })
+        end,
+        name = '87 test before_regex with a specific string length',
+        key = [[123456]],
+        before = [[    some text before| ]],
+        after = [[    some text before123456|789 ]],
+    },
 }
 
 local run_data = _G.Test_filter(data)