diff --git a/doc/9-object-types.md b/doc/9-object-types.md
index 0629ea6f6..0dda7f9c1 100644
--- a/doc/9-object-types.md
+++ b/doc/9-object-types.md
@@ -779,12 +779,6 @@ by Icinga Web 2 in the table above.
 In addition to the category flags listed above the `DbCatEverything`
 flag may be used as a shortcut for listing all flags.
 
-> **Note**
->
-> The previous way of defining the `categories` attribute e.g.
-> `DbCatProgramStatus | DbCatState` was deprecated in 2.5 and will
-> be removed in future versions.
-
 ## <a id="objecttype-idopgsqlconnection"></a> IdoPgSqlConnection
 
 IDO database adapter for PostgreSQL.
@@ -868,13 +862,6 @@ by Icinga Web 2 in the table above.
 In addition to the category flags listed above the `DbCatEverything`
 flag may be used as a shortcut for listing all flags.
 
-> **Note**
->
-> The previous way of defining the `categories` attribute e.g.
-> `DbCatProgramStatus | DbCatState` was deprecated in 2.5 and will
-> be removed in future versions.
-
-
 ## <a id="objecttype-influxdbwriter"></a> InfluxdbWriter
 
 Writes check result metrics and performance data to a defined InfluxDB host.
diff --git a/lib/db_ido/dbconnection.cpp b/lib/db_ido/dbconnection.cpp
index e27e18cb1..63ed62c6f 100644
--- a/lib/db_ido/dbconnection.cpp
+++ b/lib/db_ido/dbconnection.cpp
@@ -48,15 +48,7 @@ void DbConnection::OnConfigLoaded(void)
 
 	Value categories = GetCategories();
 
-	//TODO: Remove 'cat1 | cat2' notation in 2.6
-	if (categories.IsNumber()) {
-		SetCategoryFilter(categories);
-		Log(LogWarning, "DbConnection")
-		    << "Specifying flags using '|' for 'categories' for object '" << GetName()
-		    << "' of type '" << GetReflectionType()->GetName() << "'"
-		    << " is deprecated. This functionality will be removed in 2.6.0. Please use an array.";
-	} else
-		SetCategoryFilter(FilterArrayToInt(categories, DbQuery::GetCategoryFilterMap(), DbCatEverything));
+	SetCategoryFilter(FilterArrayToInt(categories, DbQuery::GetCategoryFilterMap(), DbCatEverything));
 
 	if (!GetEnableHa()) {
 		Log(LogDebug, "DbConnection")
@@ -498,6 +490,19 @@ void DbConnection::ValidateFailoverTimeout(double value, const ValidationUtils&
 		BOOST_THROW_EXCEPTION(ValidationError(this, boost::assign::list_of("failover_timeout"), "Failover timeout minimum is 60s."));
 }
 
+void DbConnection::ValidateCategories(const Array::Ptr& value, const ValidationUtils& utils)
+{
+	ObjectImpl<DbConnection>::ValidateCategories(value, utils);
+
+	int filter = FilterArrayToInt(value, DbQuery::GetCategoryFilterMap(), 0);
+
+	if (filter == -1 || (filter & ~(DbCatInvalid | DbCatEverything | DbCatConfig | DbCatState |
+	    DbCatAcknowledgement | DbCatComment | DbCatDowntime | DbCatEventHandler | DbCatExternalCommand |
+	    DbCatFlapping | DbCatLog | DbCatNotification | DbCatProgramStatus | DbCatRetention |
+	    DbCatStateHistory)) != 0)
+		BOOST_THROW_EXCEPTION(ValidationError(this, boost::assign::list_of("categories"), "categories filter is invalid."));
+}
+
 void DbConnection::IncreaseQueryCount(void)
 {
 	double now = Utility::GetTime();
diff --git a/lib/db_ido/dbconnection.hpp b/lib/db_ido/dbconnection.hpp
index 08933b5d7..b87ada851 100644
--- a/lib/db_ido/dbconnection.hpp
+++ b/lib/db_ido/dbconnection.hpp
@@ -77,6 +77,7 @@ public:
 	virtual int GetPendingQueryCount(void) const = 0;
 
 	virtual void ValidateFailoverTimeout(double value, const ValidationUtils& utils) override;
+	virtual void ValidateCategories(const Array::Ptr& value, const ValidationUtils& utils) override;
 
 protected:
 	virtual void OnConfigLoaded(void) override;
diff --git a/lib/db_ido/dbconnection.ti b/lib/db_ido/dbconnection.ti
index 77d50f6e5..cf922bd79 100644
--- a/lib/db_ido/dbconnection.ti
+++ b/lib/db_ido/dbconnection.ti
@@ -35,7 +35,7 @@ abstract class DbConnection : ConfigObject
 		default {{{ return new Dictionary(); }}}
 	};
 
-	[config] Value categories {
+	[config] Array::Ptr categories {
 		default {{{
 			Array::Ptr cat = new Array();
 			cat->Add("DbCatConfig");
@@ -90,10 +90,8 @@ validator DbConnection {
 		Number systemcommands_age;
 	};
 
-	Number categories;
 	Array categories {
 		String "*";
-		Number "*";
 	};
 };