diff --git a/changelog/unreleased/kong/fix-reports-uninitialized-variable-in-400.yml b/changelog/unreleased/kong/fix-reports-uninitialized-variable-in-400.yml
new file mode 100644
index 000000000000..398af4beb460
--- /dev/null
+++ b/changelog/unreleased/kong/fix-reports-uninitialized-variable-in-400.yml
@@ -0,0 +1,4 @@
+message: |
+  Fixed an issue where unnecessary uninitialized variable error log is reported when 400 bad requests were received.
+type: bugfix
+scope: Core
diff --git a/kong/reports.lua b/kong/reports.lua
index edb1e236b1fe..f9c470c73d43 100644
--- a/kong/reports.lua
+++ b/kong/reports.lua
@@ -335,6 +335,12 @@ function get_current_suffix(ctx)
     return nil
   end
 
+  -- 400 case is for invalid requests, eg: if a client sends a HTTP
+  -- request to a HTTPS port, it does not initialized any Nginx variables
+  if proxy_mode == "" and kong.response.get_status() == 400 then
+    return nil
+  end
+
   log(WARN, "could not determine log suffix (scheme=", tostring(scheme),
             ", proxy_mode=", tostring(proxy_mode), ")")
 end
diff --git a/kong/templates/nginx_kong.lua b/kong/templates/nginx_kong.lua
index 1f1c2803c463..0babc66bf5e2 100644
--- a/kong/templates/nginx_kong.lua
+++ b/kong/templates/nginx_kong.lua
@@ -62,6 +62,8 @@ ssl_ciphers ${{SSL_CIPHERS}};
 $(el.name) $(el.value);
 > end
 
+uninitialized_variable_warn  off;
+
 init_by_lua_block {
 > if test and coverage then
     require 'luacov'
@@ -441,9 +443,8 @@ server {
 
     location = /kong_error_handler {
         internal;
-        default_type                 '';
 
-        uninitialized_variable_warn  off;
+        default_type                 '';
 
         rewrite_by_lua_block {;}
         access_by_lua_block  {;}
diff --git a/spec/02-integration/05-proxy/22-reports_spec.lua b/spec/02-integration/05-proxy/22-reports_spec.lua
index a34de814d5c4..25f20bbefbee 100644
--- a/spec/02-integration/05-proxy/22-reports_spec.lua
+++ b/spec/02-integration/05-proxy/22-reports_spec.lua
@@ -249,6 +249,20 @@ for _, strategy in helpers.each_strategy() do
       proxy_ssl_client:close()
     end)
 
+    it("when send http request to https port, no other error in error.log", function()
+      local https_port = assert(helpers.get_proxy_port(true))
+      local proxy_client = assert(helpers.proxy_client(nil, https_port))
+      local res = proxy_client:get("/", {
+        headers = { host  = "http-service.test" }
+      })
+      reports_send_ping({port=constants.REPORTS.STATS_TLS_PORT})
+
+      assert.response(res).has_status(400)
+      assert.logfile().has.no.line("using uninitialized")
+      assert.logfile().has.no.line("could not determine log suffix (scheme=http, proxy_mode=)")
+      proxy_client:close()
+    end)
+
     it("reports h2c requests #h2_client", function()
       local h2c_client = assert(helpers.proxy_client_h2c())
       local body, headers = h2c_client({