diff --git a/ast.go b/ast.go
index 441e7c4..bf788cf 100644
--- a/ast.go
+++ b/ast.go
@@ -689,6 +689,7 @@ type UpsertClause struct {
 
 	DoNothing       bool          // position of NOTHING keyword after DO
 	DoUpdate        bool          // position of UPDATE keyword after DO
+	DuplicateKey    bool          // position of ON DUPLICATE KEY UPDATE keyword
 	Assignments     []*Assignment // list of column assignments
 	UpdateWhereExpr Expr          // optional conditional expression for DO UPDATE SET
 }
@@ -696,40 +697,49 @@ type UpsertClause struct {
 // String returns the string representation of the clause.
 func (c *UpsertClause) String() string {
 	var buf bytes.Buffer
-	buf.WriteString("ON CONFLICT")
-
-	if len(c.Columns) != 0 {
-		buf.WriteString(" (")
-		for i, col := range c.Columns {
+	if c.DuplicateKey {
+		buf.WriteString("ON DUPLICATE KEY UPDATE ")
+		for i := range c.Assignments {
 			if i != 0 {
 				buf.WriteString(", ")
 			}
-			buf.WriteString(col.String())
+			buf.WriteString(c.Assignments[i].String())
 		}
-		buf.WriteString(")")
+	} else {
+		buf.WriteString("ON CONFLICT")
 
-		if c.WhereExpr != nil {
-			fmt.Fprintf(&buf, " WHERE %s", c.WhereExpr.String())
-		}
-	}
+		if len(c.Columns) != 0 {
+			buf.WriteString(" (")
+			for i, col := range c.Columns {
+				if i != 0 {
+					buf.WriteString(", ")
+				}
+				buf.WriteString(col.String())
+			}
+			buf.WriteString(")")
 
-	buf.WriteString(" DO")
-	if c.DoNothing {
-		buf.WriteString(" NOTHING")
-	} else {
-		buf.WriteString(" UPDATE SET ")
-		for i := range c.Assignments {
-			if i != 0 {
-				buf.WriteString(", ")
+			if c.WhereExpr != nil {
+				fmt.Fprintf(&buf, " WHERE %s", c.WhereExpr.String())
 			}
-			buf.WriteString(c.Assignments[i].String())
 		}
 
-		if c.UpdateWhereExpr != nil {
-			fmt.Fprintf(&buf, " WHERE %s", c.UpdateWhereExpr.String())
+		buf.WriteString(" DO")
+		if c.DoNothing {
+			buf.WriteString(" NOTHING")
+		} else {
+			buf.WriteString(" UPDATE SET ")
+			for i := range c.Assignments {
+				if i != 0 {
+					buf.WriteString(", ")
+				}
+				buf.WriteString(c.Assignments[i].String())
+			}
+
+			if c.UpdateWhereExpr != nil {
+				fmt.Fprintf(&buf, " WHERE %s", c.UpdateWhereExpr.String())
+			}
 		}
 	}
-
 	return buf.String()
 }
 
diff --git a/parser.go b/parser.go
index d11fef3..e308815 100644
--- a/parser.go
+++ b/parser.go
@@ -212,8 +212,12 @@ func (p *Parser) parseUpsertClause() (_ *UpsertClause, err error) {
 
 	// Parse "ON CONFLICT"
 	p.lex()
-	if p.peek() != CONFLICT {
-		return &clause, p.errorExpected(p.pos, p.tok, "CONFLICT")
+	switch p.peek() {
+	case CONFLICT:
+	case DUPLICATE:
+		clause.DuplicateKey = true
+	default:
+		return &clause, p.errorExpected(p.pos, p.tok, "CONFLICT or DUPLICATE")
 	}
 	p.lex()
 
@@ -244,9 +248,11 @@ func (p *Parser) parseUpsertClause() (_ *UpsertClause, err error) {
 		}
 	}
 
-	// Parse "DO NOTHING" or "DO UPDATE SET".
-	if p.peek() != DO {
+	// Parse "DO NOTHING" or "DO UPDATE SET" or "ON DUPLICATE KEY".
+	if !clause.DuplicateKey && p.peek() != DO {
 		return &clause, p.errorExpected(p.pos, p.tok, "DO")
+	} else if clause.DuplicateKey && p.peek() != KEY {
+		return &clause, p.errorExpected(p.pos, p.tok, "KEY")
 	}
 	p.lex()
 
@@ -262,10 +268,12 @@ func (p *Parser) parseUpsertClause() (_ *UpsertClause, err error) {
 	// Otherwise parse "UPDATE SET"
 	p.lex()
 	clause.DoUpdate = true
-	if p.peek() != SET {
-		return &clause, p.errorExpected(p.pos, p.tok, "SET")
+	if !clause.DuplicateKey {
+		if p.peek() != SET {
+			return &clause, p.errorExpected(p.pos, p.tok, "SET")
+		}
+		p.lex()
 	}
-	p.lex()
 
 	// Parse list of assignments.
 	for {
diff --git a/token.go b/token.go
index c58b20a..89bfb57 100644
--- a/token.go
+++ b/token.go
@@ -233,6 +233,7 @@ const (
 	WINDOW
 	WITH
 	WITHOUT
+	DUPLICATE
 	keyword_end
 
 	ANY // ???
@@ -444,6 +445,7 @@ var tokens = [...]string{
 	WINDOW:            "WINDOW",
 	WITH:              "WITH",
 	WITHOUT:           "WITHOUT",
+	DUPLICATE:         "DUPLICATE",
 }
 
 func (tok Token) String() string {