diff --git a/pgproto3/bind.go b/pgproto3/bind.go
index b32cd81ca..ad6ac48bf 100644
--- a/pgproto3/bind.go
+++ b/pgproto3/bind.go
@@ -5,7 +5,9 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -116,11 +118,17 @@ func (src *Bind) Encode(dst []byte) ([]byte, error) {
 	dst = append(dst, src.PreparedStatement...)
 	dst = append(dst, 0)
 
+	if len(src.ParameterFormatCodes) > math.MaxUint16 {
+		return nil, errors.New("too many parameter format codes")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ParameterFormatCodes)))
 	for _, fc := range src.ParameterFormatCodes {
 		dst = pgio.AppendInt16(dst, fc)
 	}
 
+	if len(src.Parameters) > math.MaxUint16 {
+		return nil, errors.New("too many parameters")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.Parameters)))
 	for _, p := range src.Parameters {
 		if p == nil {
@@ -132,6 +140,9 @@ func (src *Bind) Encode(dst []byte) ([]byte, error) {
 		dst = append(dst, p...)
 	}
 
+	if len(src.ResultFormatCodes) > math.MaxUint16 {
+		return nil, errors.New("too many result format codes")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ResultFormatCodes)))
 	for _, fc := range src.ResultFormatCodes {
 		dst = pgio.AppendInt16(dst, fc)
diff --git a/pgproto3/copy_both_response.go b/pgproto3/copy_both_response.go
index dbbd8e15c..99e1afea4 100644
--- a/pgproto3/copy_both_response.go
+++ b/pgproto3/copy_both_response.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -47,6 +48,9 @@ func (dst *CopyBothResponse) Decode(src []byte) error {
 func (src *CopyBothResponse) Encode(dst []byte) ([]byte, error) {
 	dst, sp := beginMessage(dst, 'W')
 	dst = append(dst, src.OverallFormat)
+	if len(src.ColumnFormatCodes) > math.MaxUint16 {
+		return nil, errors.New("too many column format codes")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ColumnFormatCodes)))
 	for _, fc := range src.ColumnFormatCodes {
 		dst = pgio.AppendUint16(dst, fc)
diff --git a/pgproto3/copy_in_response.go b/pgproto3/copy_in_response.go
index 0a772afa0..06cf99ced 100644
--- a/pgproto3/copy_in_response.go
+++ b/pgproto3/copy_in_response.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -48,6 +49,9 @@ func (src *CopyInResponse) Encode(dst []byte) ([]byte, error) {
 	dst, sp := beginMessage(dst, 'G')
 
 	dst = append(dst, src.OverallFormat)
+	if len(src.ColumnFormatCodes) > math.MaxUint16 {
+		return nil, errors.New("too many column format codes")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ColumnFormatCodes)))
 	for _, fc := range src.ColumnFormatCodes {
 		dst = pgio.AppendUint16(dst, fc)
diff --git a/pgproto3/copy_out_response.go b/pgproto3/copy_out_response.go
index 40525da62..549e916c1 100644
--- a/pgproto3/copy_out_response.go
+++ b/pgproto3/copy_out_response.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -48,6 +49,9 @@ func (src *CopyOutResponse) Encode(dst []byte) ([]byte, error) {
 
 	dst = append(dst, src.OverallFormat)
 
+	if len(src.ColumnFormatCodes) > math.MaxUint16 {
+		return nil, errors.New("too many column format codes")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ColumnFormatCodes)))
 	for _, fc := range src.ColumnFormatCodes {
 		dst = pgio.AppendUint16(dst, fc)
diff --git a/pgproto3/data_row.go b/pgproto3/data_row.go
index cbc76dc24..fdfb0f7f6 100644
--- a/pgproto3/data_row.go
+++ b/pgproto3/data_row.go
@@ -4,6 +4,8 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -66,6 +68,9 @@ func (dst *DataRow) Decode(src []byte) error {
 func (src *DataRow) Encode(dst []byte) ([]byte, error) {
 	dst, sp := beginMessage(dst, 'D')
 
+	if len(src.Values) > math.MaxUint16 {
+		return nil, errors.New("too many values")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.Values)))
 	for _, v := range src.Values {
 		if v == nil {
diff --git a/pgproto3/function_call.go b/pgproto3/function_call.go
index 0b15fce23..7d83579ff 100644
--- a/pgproto3/function_call.go
+++ b/pgproto3/function_call.go
@@ -2,6 +2,8 @@ package pgproto3
 
 import (
 	"encoding/binary"
+	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -74,10 +76,18 @@ func (dst *FunctionCall) Decode(src []byte) error {
 func (src *FunctionCall) Encode(dst []byte) ([]byte, error) {
 	dst, sp := beginMessage(dst, 'F')
 	dst = pgio.AppendUint32(dst, src.Function)
+
+	if len(src.ArgFormatCodes) > math.MaxUint16 {
+		return nil, errors.New("too many arg format codes")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ArgFormatCodes)))
 	for _, argFormatCode := range src.ArgFormatCodes {
 		dst = pgio.AppendUint16(dst, argFormatCode)
 	}
+
+	if len(src.Arguments) > math.MaxUint16 {
+		return nil, errors.New("too many arguments")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.Arguments)))
 	for _, argument := range src.Arguments {
 		if argument == nil {
diff --git a/pgproto3/parameter_description.go b/pgproto3/parameter_description.go
index 685e04b8c..1ef27b75f 100644
--- a/pgproto3/parameter_description.go
+++ b/pgproto3/parameter_description.go
@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/json"
+	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -42,6 +44,9 @@ func (dst *ParameterDescription) Decode(src []byte) error {
 func (src *ParameterDescription) Encode(dst []byte) ([]byte, error) {
 	dst, sp := beginMessage(dst, 't')
 
+	if len(src.ParameterOIDs) > math.MaxUint16 {
+		return nil, errors.New("too many parameter oids")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ParameterOIDs)))
 	for _, oid := range src.ParameterOIDs {
 		dst = pgio.AppendUint32(dst, oid)
diff --git a/pgproto3/parse.go b/pgproto3/parse.go
index a59154cda..6ba3486cf 100644
--- a/pgproto3/parse.go
+++ b/pgproto3/parse.go
@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/json"
+	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -60,6 +62,9 @@ func (src *Parse) Encode(dst []byte) ([]byte, error) {
 	dst = append(dst, src.Query...)
 	dst = append(dst, 0)
 
+	if len(src.ParameterOIDs) > math.MaxUint16 {
+		return nil, errors.New("too many parameter oids")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.ParameterOIDs)))
 	for _, oid := range src.ParameterOIDs {
 		dst = pgio.AppendUint32(dst, oid)
diff --git a/pgproto3/row_description.go b/pgproto3/row_description.go
index c68f1d466..dc2a4ddf2 100644
--- a/pgproto3/row_description.go
+++ b/pgproto3/row_description.go
@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/json"
+	"errors"
+	"math"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
 )
@@ -102,6 +104,9 @@ func (dst *RowDescription) Decode(src []byte) error {
 func (src *RowDescription) Encode(dst []byte) ([]byte, error) {
 	dst, sp := beginMessage(dst, 'T')
 
+	if len(src.Fields) > math.MaxUint16 {
+		return nil, errors.New("too many fields")
+	}
 	dst = pgio.AppendUint16(dst, uint16(len(src.Fields)))
 	for _, fd := range src.Fields {
 		dst = append(dst, fd.Name...)