diff --git a/internal/parser/planparserv2/plan_parser_v2.go b/internal/parser/planparserv2/plan_parser_v2.go
index 210ee57c8b..17cf00b555 100644
--- a/internal/parser/planparserv2/plan_parser_v2.go
+++ b/internal/parser/planparserv2/plan_parser_v2.go
@@ -17,13 +17,26 @@ func handleExpr(schema *typeutil.SchemaHelper, exprStr string) interface{} {
 
 	inputStream := antlr.NewInputStream(exprStr)
 	errorListener := &errorListener{}
-	parser := getParser(inputStream, errorListener)
+
+	lexer := getLexer(inputStream, errorListener)
+	if errorListener.err != nil {
+		return errorListener.err
+	}
+
+	parser := getParser(lexer, errorListener)
+	if errorListener.err != nil {
+		return errorListener.err
+	}
 
 	ast := parser.Expr()
 	if errorListener.err != nil {
 		return errorListener.err
 	}
 
+	// lexer & parser won't be used by this thread, can be put into pool.
+	putLexer(lexer)
+	putParser(parser)
+
 	visitor := NewParserVisitor(schema)
 	return ast.Accept(visitor)
 }
diff --git a/internal/parser/planparserv2/plan_parser_v2_test.go b/internal/parser/planparserv2/plan_parser_v2_test.go
index 3d04591051..14f0cc1d61 100644
--- a/internal/parser/planparserv2/plan_parser_v2_test.go
+++ b/internal/parser/planparserv2/plan_parser_v2_test.go
@@ -1,6 +1,7 @@
 package planparserv2
 
 import (
+	"sync"
 	"testing"
 
 	"github.com/milvus-io/milvus/internal/proto/planpb"
@@ -488,3 +489,45 @@ func TestCreateSearchPlan_Invalid(t *testing.T) {
 		assert.Error(t, err)
 	})
 }
+
+func Test_handleExpr(t *testing.T) {
+	schema := newTestSchema()
+	schemaHelper, err := typeutil.CreateSchemaHelper(schema)
+	assert.NoError(t, err)
+
+	ret1 := handleExpr(schemaHelper, "this is not a normal expression")
+	err1, ok := ret1.(error)
+	assert.True(t, ok)
+	assert.Error(t, err1)
+}
+
+// test if handleExpr is thread-safe.
+func Test_handleExpr_17126(t *testing.T) {
+	schema := newTestSchema()
+	schemaHelper, err := typeutil.CreateSchemaHelper(schema)
+	assert.NoError(t, err)
+	normal := "Int64Field > 0"
+	abnormal := "this is not a normal expression"
+
+	n := 4 // default parallel in regression.
+	m := 16
+	var wg sync.WaitGroup
+	for i := 0; i < n*m; i++ {
+		wg.Add(1)
+		i := i
+		go func() {
+			defer wg.Done()
+			if i%2 == 0 {
+				ret := handleExpr(schemaHelper, normal)
+				_, ok := ret.(error)
+				assert.False(t, ok)
+			} else {
+				ret := handleExpr(schemaHelper, abnormal)
+				err, ok := ret.(error)
+				assert.True(t, ok)
+				assert.Error(t, err)
+			}
+		}()
+	}
+	wg.Wait()
+}
diff --git a/internal/parser/planparserv2/pool.go b/internal/parser/planparserv2/pool.go
index 0a81106bef..005884b60e 100644
--- a/internal/parser/planparserv2/pool.go
+++ b/internal/parser/planparserv2/pool.go
@@ -25,26 +25,33 @@ func getLexer(stream *antlr.InputStream, listeners ...antlr.ErrorListener) *antl
 	if !ok {
 		lexer = antlrparser.NewPlanLexer(nil)
 	}
-	lexer.SetInputStream(stream)
 	for _, listener := range listeners {
 		lexer.AddErrorListener(listener)
 	}
-	lexerPool.Put(lexer)
+	lexer.SetInputStream(stream)
 	return lexer
 }
 
-func getParser(stream *antlr.InputStream, listeners ...antlr.ErrorListener) *antlrparser.PlanParser {
-	lexer := getLexer(stream, listeners...)
+func getParser(lexer *antlrparser.PlanLexer, listeners ...antlr.ErrorListener) *antlrparser.PlanParser {
 	tokenStream := antlr.NewCommonTokenStream(lexer, antlr.TokenDefaultChannel)
 	parser, ok := parserPool.Get().(*antlrparser.PlanParser)
 	if !ok {
 		parser = antlrparser.NewPlanParser(nil)
 	}
-	parser.SetInputStream(tokenStream)
-	parser.BuildParseTrees = true
 	for _, listener := range listeners {
 		parser.AddErrorListener(listener)
 	}
-	parserPool.Put(parser)
+	parser.BuildParseTrees = true
+	parser.SetInputStream(tokenStream)
 	return parser
 }
+
+func putLexer(lexer *antlrparser.PlanLexer) {
+	lexer.SetInputStream(nil)
+	lexerPool.Put(lexer)
+}
+
+func putParser(parser *antlrparser.PlanParser) {
+	parser.SetInputStream(nil)
+	parserPool.Put(parser)
+}
diff --git a/internal/parser/planparserv2/pool_test.go b/internal/parser/planparserv2/pool_test.go
index 9e238d8bbc..8c0f5b929b 100644
--- a/internal/parser/planparserv2/pool_test.go
+++ b/internal/parser/planparserv2/pool_test.go
@@ -25,11 +25,15 @@ func Test_getLexer(t *testing.T) {
 }
 
 func Test_getParser(t *testing.T) {
+	var lexer *antlrparser.PlanLexer
 	var parser *antlrparser.PlanParser
 
-	parser = getParser(genNaiveInputStream(), &errorListener{})
+	lexer = getLexer(genNaiveInputStream(), &errorListener{})
+	assert.NotNil(t, lexer)
+
+	parser = getParser(lexer, &errorListener{})
 	assert.NotNil(t, parser)
 
-	parser = getParser(genNaiveInputStream(), &errorListener{})
+	parser = getParser(lexer, &errorListener{})
 	assert.NotNil(t, parser)
 }