diff --git a/ngcp/dlgcnt.lua b/ngcp/dlgcnt.lua
index 159b10f..016363d 100644
--- a/ngcp/dlgcnt.lua
+++ b/ngcp/dlgcnt.lua
@@ -53,7 +53,8 @@ end
                     port = 6379,
                     db = "4"
                 },
-                check_pair_dup = false
+                check_pair_dup = false,
+                allow_negative = false
             },
             central = {},
             pair = {}
@@ -80,6 +81,9 @@ end
         if res == 0 then
             self.central:del(key);
             sr.log("dbg", string.format("central:del[%s] counter is 0\n", key));
+        elseif res < 0 and not self.config.allow_negative then
+            self.central:del(key);
+            sr.log("warn", string.format("central:del[%s] counter was %s\n", key, tostring(res)));
         else
             sr.log("dbg", string.format("central:decr[%s]=>[%s]\n", key, tostring(res)));
         end
diff --git a/tests/ngcp_dlgcnt.lua b/tests/ngcp_dlgcnt.lua
index 7626689..55812b3 100644
--- a/tests/ngcp_dlgcnt.lua
+++ b/tests/ngcp_dlgcnt.lua
@@ -132,6 +132,61 @@ TestNGCPDlgCnt = {} --class
         assertIs(self.dlg.pair, self.pair)
     end
 
+    function TestNGCPDlgCnt:test_del_zero()
+        local c = self.dlg.config
+        self.pair:ping() ;mc :returns(true)
+        self.pair:lpop("callid0") ;mc :returns("total")
+        self.pair:lpop("callid0") ;mc :returns(nil)
+        self.central:del("total") ;mc :returns(true)
+
+        self.central:ping() ;mc :returns(true)
+        self.central:decr("total")  ;mc :returns(0)
+
+        mc:replay()
+        self.dlg:del("callid0")
+        mc:verify()
+
+        assertIs(self.dlg.central, self.central)
+        assertIs(self.dlg.pair, self.pair)
+    end
+
+    function TestNGCPDlgCnt:test_del_negative()
+        local c = self.dlg.config
+        c.allow_negative = false
+        self.pair:ping() ;mc :returns(true)
+        self.pair:lpop("callid0") ;mc :returns("total")
+        self.pair:lpop("callid0") ;mc :returns(nil)
+
+        self.central:ping() ;mc :returns(true)
+        self.central:decr("total")  ;mc :returns(-1)
+        self.central:del("total") ;mc :returns(true)
+
+        mc:replay()
+        self.dlg:del("callid0")
+        mc:verify()
+
+        assertIs(self.dlg.central, self.central)
+        assertIs(self.dlg.pair, self.pair)
+    end
+
+    function TestNGCPDlgCnt:test_del_negative_ok()
+        local c = self.dlg.config
+        c.allow_negative = true
+        self.pair:ping() ;mc :returns(true)
+        self.pair:lpop("callid0") ;mc :returns("total")
+        self.pair:lpop("callid0") ;mc :returns(nil)
+
+        self.central:ping() ;mc :returns(true)
+        self.central:decr("total")  ;mc :returns(-1)
+
+        mc:replay()
+        self.dlg:del("callid0")
+        mc:verify()
+
+        assertIs(self.dlg.central, self.central)
+        assertIs(self.dlg.pair, self.pair)
+    end
+
     function TestNGCPDlgCnt:test_del_multy()
         local c = self.dlg.config
         self.pair:ping() ;mc :returns(true)