diff --git a/src/common/classes/Nullable.h b/src/common/classes/Nullable.h
index a83798cf5d..46fe099c8e 100644
--- a/src/common/classes/Nullable.h
+++ b/src/common/classes/Nullable.h
@@ -39,28 +39,6 @@ public:
 	}
 };
 
-// NullableClear specializations.
-
-template <>
-class NullableClear<Firebird::string>	// string especialization for NullableClear
-{
-public:
-	static void clear(Firebird::string& v)
-	{
-		v = "";
-	}
-};
-
-template <>
-class NullableClear<Firebird::MetaName>	// MetaName especialization for NullableClear
-{
-public:
-	static void clear(Firebird::MetaName& v)
-	{
-		v = "";
-	}
-};
-
 
 // Nullable support without constructor, to allow usage in unions (used in the parser).
 template <typename T> class BaseNullable
@@ -93,6 +71,39 @@ public:
 };
 
 
+// NullableClear specializations.
+
+template <>
+class NullableClear<Firebird::string>	// string especialization for NullableClear
+{
+public:
+	static void clear(Firebird::string& v)
+	{
+		v = "";
+	}
+};
+
+template <>
+class NullableClear<Firebird::MetaName>	// MetaName especialization for NullableClear
+{
+public:
+	static void clear(Firebird::MetaName& v)
+	{
+		v = "";
+	}
+};
+
+template <typename T>
+class NullableClear<BaseNullable<T> >
+{
+public:
+	static void clear(BaseNullable<T>& v)
+	{
+		v.specified = false;
+	}
+};
+
+
 // Actual Nullable template.
 template <typename T> class Nullable : public BaseNullable<T>
 {
diff --git a/src/dsql/DdlNodes.epp b/src/dsql/DdlNodes.epp
index 8dd8aa8432..fe4dfbce3d 100644
--- a/src/dsql/DdlNodes.epp
+++ b/src/dsql/DdlNodes.epp
@@ -4941,7 +4941,7 @@ bool CreateAlterSequenceNode::executeAlter(thread_db* tdbb, DsqlCompilerScratch*
 
 		executeDdlTrigger(tdbb, dsqlScratch, transaction, DTW_BEFORE, DDL_TRIGGER_ALTER_SEQUENCE, name);
 
-		fb_assert(value.specified);
+		fb_assert(restartSpecified && value.specified);
 		const SINT64 val = value.specified ? value.value : 0;
 		if (step.specified)
 		{
@@ -4981,8 +4981,7 @@ bool CreateAlterSequenceNode::executeAlter(thread_db* tdbb, DsqlCompilerScratch*
 		}
 
 		const SLONG id = X.RDB$GENERATOR_ID;
-		const SINT64 val = value.specified ?
-			value.value : (!X.RDB$INITIAL_VALUE.NULL ? X.RDB$INITIAL_VALUE : 0);
+
 		if (step.specified)
 		{
 			const SLONG newStep = step.value;
@@ -4997,7 +4996,13 @@ bool CreateAlterSequenceNode::executeAlter(thread_db* tdbb, DsqlCompilerScratch*
 			}
 		}
 
-		transaction->getGenIdCache()->put(id, val);
+		if (restartSpecified)
+		{
+			const SINT64 val = value.specified ?
+				value.value : (!X.RDB$INITIAL_VALUE.NULL ? X.RDB$INITIAL_VALUE : 0);
+			transaction->getGenIdCache()->put(id, val);
+		}
+
 		dsc desc;
 		desc.makeText((USHORT) name.length(), ttype_metadata, (UCHAR*) name.c_str());
 		DFW_post_work(transaction, dfw_set_generator, &desc, id);
diff --git a/src/dsql/DdlNodes.h b/src/dsql/DdlNodes.h
index 60b8bea952..5553200c95 100644
--- a/src/dsql/DdlNodes.h
+++ b/src/dsql/DdlNodes.h
@@ -916,6 +916,7 @@ public:
 		  create(true),
 		  alter(false),
 		  legacy(false),
+		  restartSpecified(false),
 		  name(pool, aName),
 		  value(aValue),
 		  step(aStep)
@@ -959,6 +960,7 @@ public:
 	bool create;
 	bool alter;
 	bool legacy;
+	bool restartSpecified;
 	const Firebird::MetaName name;
 	const BaseNullable<SINT64> value;
 	const BaseNullable<SLONG> step;
diff --git a/src/dsql/parse.y b/src/dsql/parse.y
index ad62dad7d5..b5baff0ed5 100644
--- a/src/dsql/parse.y
+++ b/src/dsql/parse.y
@@ -607,6 +607,7 @@ using namespace Firebird;
 	SINT64 int64Val;
 	FB_UINT64 uint64Val;
 	BaseNullable<SINT64> nullableInt64Val;
+	BaseNullable<BaseNullable<SINT64> > nullableNullableInt64Val;
 	BaseNullable<FB_UINT64> nullableUint64Val;
 	Jrd::ScaledNumber scaledNumber;
 	UCHAR blrOp;
@@ -1508,6 +1509,7 @@ replace_sequence_clause
 		{
 			CreateAlterSequenceNode* node = newNode<CreateAlterSequenceNode>(*$1, $2, $3);
 			node->alter = true;
+			node->restartSpecified = true;
 			$$ = node;
 		}
 	;
@@ -1524,9 +1526,10 @@ alter_sequence_clause
 		{
 			if (!$2.specified && !$3.specified)
 				yyerrorIncompleteCmd();
-			CreateAlterSequenceNode* node = newNode<CreateAlterSequenceNode>(*$1, $2, $3);
+			CreateAlterSequenceNode* node = newNode<CreateAlterSequenceNode>(*$1, $2.value, $3);
 			node->create = false;
 			node->alter = true;
+			node->restartSpecified = $2.specified;
 			$$ = node;
 		}
 	;
@@ -1537,10 +1540,10 @@ restart_value_opt
 	| RESTART WITH sequence_value	{ $$ = Nullable<SINT64>::val($3); }
 	;
 
-%type <nullableInt64Val> restart_value_opt2
+%type <nullableNullableInt64Val> restart_value_opt2
 restart_value_opt2
-	: /* nothing */			{ $$ = Nullable<SINT64>::empty(); }
-	| restart_value_opt
+	: /* nothing */			{ $$ = Nullable<BaseNullable<SINT64> >::empty(); }
+	| restart_value_opt		{ $$ = Nullable<BaseNullable<SINT64> > ::val($1); }
 	;
 
 
@@ -1553,6 +1556,7 @@ set_generator_clause
 			node->create = false;
 			node->alter = true;
 			node->legacy = true;
+			node->restartSpecified = true;
 			$$ = node;
 		}
 	;