diff --git a/dbms/src/Common/FieldVisitors.cpp b/dbms/src/Common/FieldVisitors.cpp
index 9a437d5ffe6..c5ce10c0db4 100644
--- a/dbms/src/Common/FieldVisitors.cpp
+++ b/dbms/src/Common/FieldVisitors.cpp
@@ -130,7 +130,7 @@ String FieldVisitorToString::operator() (const DecimalField<Decimal128> & x) con
 String FieldVisitorToString::operator() (const UInt128 & x) const { return formatQuoted(UUID(x)); }
 String FieldVisitorToString::operator() (const AggregateFunctionStateData & x) const
 {
-    return "(" + formatQuoted(x.name) + ")" + formatQuoted(x.data);
+    return formatQuoted(x.data);
 }
 
 String FieldVisitorToString::operator() (const Array & x) const
diff --git a/dbms/src/DataTypes/DataTypeAggregateFunction.cpp b/dbms/src/DataTypes/DataTypeAggregateFunction.cpp
index 1855522c713..2c5516e100a 100644
--- a/dbms/src/DataTypes/DataTypeAggregateFunction.cpp
+++ b/dbms/src/DataTypes/DataTypeAggregateFunction.cpp
@@ -218,9 +218,11 @@ void DataTypeAggregateFunction::deserializeTextQuoted(IColumn & column, ReadBuff
 }
 
 
-void DataTypeAggregateFunction::deserializeWholeText(IColumn &, ReadBuffer &, const FormatSettings &) const
+void DataTypeAggregateFunction::deserializeWholeText(IColumn & column, ReadBuffer & istr, const FormatSettings &) const
 {
-    throw Exception("AggregateFunction data type cannot be read from text", ErrorCodes::NOT_IMPLEMENTED);
+    String s;
+    readStringUntilEOF(s, istr);
+    deserializeFromString(function, column, s);
 }
 
 
diff --git a/dbms/src/Functions/FunctionsConversion.h b/dbms/src/Functions/FunctionsConversion.h
index 3baca412497..3bb4a795b73 100644
--- a/dbms/src/Functions/FunctionsConversion.h
+++ b/dbms/src/Functions/FunctionsConversion.h
@@ -23,6 +23,7 @@
 #include <DataTypes/DataTypeNothing.h>
 #include <DataTypes/DataTypeUUID.h>
 #include <DataTypes/DataTypeInterval.h>
+#include <DataTypes/DataTypeAggregateFunction.h>
 #include <Formats/FormatSettings.h>
 #include <Columns/ColumnString.h>
 #include <Columns/ColumnFixedString.h>
@@ -636,7 +637,7 @@ struct ConvertImplGenericFromString
             {
                 ReadBufferFromMemory read_buffer(&chars[current_offset], offsets[i] - current_offset - 1);
 
-                data_type_to.deserializeAsTextEscaped(column_to, read_buffer, format_settings);
+                data_type_to.deserializeAsWholeText(column_to, read_buffer, format_settings);
 
                 if (!read_buffer.eof())
                     throwExceptionForIncompletelyParsedValue(read_buffer, block, result);
@@ -1668,6 +1669,21 @@ private:
             }
         };
     }
+    
+    WrapperType createAggregateFunctionWrapper(const DataTypePtr & from_type_untyped, const DataTypeAggregateFunction * to_type) const
+    {
+        /// Conversion from String through parsing.
+        if (checkAndGetDataType<DataTypeString>(from_type_untyped.get()))
+        {
+            return [] (Block & block, const ColumnNumbers & arguments, const size_t result, size_t /*input_rows_count*/)
+            {
+                ConvertImplGenericFromString::execute(block, arguments, result);
+            };
+        }
+        else
+            throw Exception{"Conversion from " + from_type_untyped->getName() + " to " + to_type->getName() +
+                " is not supported", ErrorCodes::CANNOT_CONVERT_TYPE};
+    }
 
     WrapperType createArrayWrapper(const DataTypePtr & from_type_untyped, const DataTypeArray * to_type) const
     {
@@ -2145,13 +2161,12 @@ private:
             case TypeIndex::Tuple:
                 return createTupleWrapper(from_type, checkAndGetDataType<DataTypeTuple>(to_type.get()));
 
+            case TypeIndex::AggregateFunction:
+                return createAggregateFunctionWrapper(from_type, checkAndGetDataType<DataTypeAggregateFunction>(to_type.get()));
             default:
                 break;
         }
 
-        /// It's possible to use ConvertImplGenericFromString to convert from String to AggregateFunction,
-        ///  but it is disabled because deserializing aggregate functions state might be unsafe.
-
         throw Exception{"Conversion from " + from_type->getName() + " to " + to_type->getName() + " is not supported",
             ErrorCodes::CANNOT_CONVERT_TYPE};
     }
diff --git a/dbms/src/IO/ReadHelpers.h b/dbms/src/IO/ReadHelpers.h
index 9105f593ed7..1c1d594bb83 100644
--- a/dbms/src/IO/ReadHelpers.h
+++ b/dbms/src/IO/ReadHelpers.h
@@ -39,7 +39,7 @@
 #endif
 
 
-#define DEFAULT_MAX_STRING_SIZE 0x00FFFFFFULL
+#define DEFAULT_MAX_STRING_SIZE 0x3FFFFFFFULL
 
 
 namespace DB