diff --git a/internal/errors/errors.go b/internal/errors/errors.go
index 20c17b35e..d96719829 100644
--- a/internal/errors/errors.go
+++ b/internal/errors/errors.go
@@ -87,3 +87,18 @@ func InvalidUTF8(name string) error {
 func RequiredNotSet(name string) error {
 	return New("required field %v not set", name)
 }
+
+type SizeMismatchError struct {
+	Calculated, Measured int
+}
+
+func (e *SizeMismatchError) Error() string {
+	return fmt.Sprintf("size mismatch (see https://github.com/golang/protobuf/issues/1609): calculated=%d, measured=%d", e.Calculated, e.Measured)
+}
+
+func MismatchedSizeCalculation(calculated, measured int) error {
+	return &SizeMismatchError{
+		Calculated: calculated,
+		Measured:   measured,
+	}
+}
diff --git a/internal/impl/codec_field.go b/internal/impl/codec_field.go
index 3fadd241e..e8040ef16 100644
--- a/internal/impl/codec_field.go
+++ b/internal/impl/codec_field.go
@@ -233,9 +233,15 @@ func sizeMessageInfo(p pointer, f *coderFieldInfo, opts marshalOptions) int {
 }
 
 func appendMessageInfo(b []byte, p pointer, f *coderFieldInfo, opts marshalOptions) ([]byte, error) {
+	calculatedSize := f.mi.sizePointer(p.Elem(), opts)
 	b = protowire.AppendVarint(b, f.wiretag)
-	b = protowire.AppendVarint(b, uint64(f.mi.sizePointer(p.Elem(), opts)))
-	return f.mi.marshalAppendPointer(b, p.Elem(), opts)
+	b = protowire.AppendVarint(b, uint64(calculatedSize))
+	before := len(b)
+	b, err := f.mi.marshalAppendPointer(b, p.Elem(), opts)
+	if measuredSize := len(b) - before; calculatedSize != measuredSize && err == nil {
+		return nil, errors.MismatchedSizeCalculation(calculatedSize, measuredSize)
+	}
+	return b, err
 }
 
 func consumeMessageInfo(b []byte, p pointer, wtyp protowire.Type, f *coderFieldInfo, opts unmarshalOptions) (out unmarshalOutput, err error) {
@@ -267,9 +273,15 @@ func sizeMessage(m proto.Message, tagsize int, _ marshalOptions) int {
 }
 
 func appendMessage(b []byte, m proto.Message, wiretag uint64, opts marshalOptions) ([]byte, error) {
+	calculatedSize := proto.Size(m)
 	b = protowire.AppendVarint(b, wiretag)
-	b = protowire.AppendVarint(b, uint64(proto.Size(m)))
-	return opts.Options().MarshalAppend(b, m)
+	b = protowire.AppendVarint(b, uint64(calculatedSize))
+	before := len(b)
+	b, err := opts.Options().MarshalAppend(b, m)
+	if measuredSize := len(b) - before; calculatedSize != measuredSize && err == nil {
+		return nil, errors.MismatchedSizeCalculation(calculatedSize, measuredSize)
+	}
+	return b, err
 }
 
 func consumeMessage(b []byte, m proto.Message, wtyp protowire.Type, opts unmarshalOptions) (out unmarshalOutput, err error) {
@@ -482,10 +494,14 @@ func appendMessageSliceInfo(b []byte, p pointer, f *coderFieldInfo, opts marshal
 		b = protowire.AppendVarint(b, f.wiretag)
 		siz := f.mi.sizePointer(v, opts)
 		b = protowire.AppendVarint(b, uint64(siz))
+		before := len(b)
 		b, err = f.mi.marshalAppendPointer(b, v, opts)
 		if err != nil {
 			return b, err
 		}
+		if measuredSize := len(b) - before; siz != measuredSize {
+			return nil, errors.MismatchedSizeCalculation(siz, measuredSize)
+		}
 	}
 	return b, nil
 }
@@ -538,10 +554,14 @@ func appendMessageSlice(b []byte, p pointer, wiretag uint64, goType reflect.Type
 		b = protowire.AppendVarint(b, wiretag)
 		siz := proto.Size(m)
 		b = protowire.AppendVarint(b, uint64(siz))
+		before := len(b)
 		b, err = opts.Options().MarshalAppend(b, m)
 		if err != nil {
 			return b, err
 		}
+		if measuredSize := len(b) - before; siz != measuredSize {
+			return nil, errors.MismatchedSizeCalculation(siz, measuredSize)
+		}
 	}
 	return b, nil
 }
@@ -599,11 +619,15 @@ func appendMessageSliceValue(b []byte, listv protoreflect.Value, wiretag uint64,
 		b = protowire.AppendVarint(b, wiretag)
 		siz := proto.Size(m)
 		b = protowire.AppendVarint(b, uint64(siz))
+		before := len(b)
 		var err error
 		b, err = mopts.MarshalAppend(b, m)
 		if err != nil {
 			return b, err
 		}
+		if measuredSize := len(b) - before; siz != measuredSize {
+			return nil, errors.MismatchedSizeCalculation(siz, measuredSize)
+		}
 	}
 	return b, nil
 }
diff --git a/internal/impl/codec_map.go b/internal/impl/codec_map.go
index 111b9d16f..fb35f0bae 100644
--- a/internal/impl/codec_map.go
+++ b/internal/impl/codec_map.go
@@ -9,6 +9,7 @@ import (
 	"sort"
 
 	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/internal/errors"
 	"google.golang.org/protobuf/internal/genid"
 	"google.golang.org/protobuf/reflect/protoreflect"
 )
@@ -240,11 +241,16 @@ func appendMapItem(b []byte, keyrv, valrv reflect.Value, mapi *mapInfo, f *coder
 		size += mapi.keyFuncs.size(key.Value(), mapKeyTagSize, opts)
 		size += mapi.valFuncs.size(val, mapValTagSize, opts)
 		b = protowire.AppendVarint(b, uint64(size))
+		before := len(b)
 		b, err := mapi.keyFuncs.marshal(b, key.Value(), mapi.keyWiretag, opts)
 		if err != nil {
 			return nil, err
 		}
-		return mapi.valFuncs.marshal(b, val, mapi.valWiretag, opts)
+		b, err = mapi.valFuncs.marshal(b, val, mapi.valWiretag, opts)
+		if measuredSize := len(b) - before; size != measuredSize && err == nil {
+			return nil, errors.MismatchedSizeCalculation(size, measuredSize)
+		}
+		return b, err
 	} else {
 		key := mapi.conv.keyConv.PBValueOf(keyrv).MapKey()
 		val := pointerOfValue(valrv)
@@ -259,7 +265,12 @@ func appendMapItem(b []byte, keyrv, valrv reflect.Value, mapi *mapInfo, f *coder
 		}
 		b = protowire.AppendVarint(b, mapi.valWiretag)
 		b = protowire.AppendVarint(b, uint64(valSize))
-		return f.mi.marshalAppendPointer(b, val, opts)
+		before := len(b)
+		b, err = f.mi.marshalAppendPointer(b, val, opts)
+		if measuredSize := len(b) - before; valSize != measuredSize && err == nil {
+			return nil, errors.MismatchedSizeCalculation(valSize, measuredSize)
+		}
+		return b, err
 	}
 }
 
diff --git a/proto/encode.go b/proto/encode.go
index 5f69539cb..c779f6dfc 100644
--- a/proto/encode.go
+++ b/proto/encode.go
@@ -5,12 +5,17 @@
 package proto
 
 import (
+	"errors"
+	"fmt"
+
 	"google.golang.org/protobuf/encoding/protowire"
 	"google.golang.org/protobuf/internal/encoding/messageset"
 	"google.golang.org/protobuf/internal/order"
 	"google.golang.org/protobuf/internal/pragma"
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/runtime/protoiface"
+
+	protoerrors "google.golang.org/protobuf/internal/errors"
 )
 
 // MarshalOptions configures the marshaler.
@@ -175,6 +180,10 @@ func (o MarshalOptions) marshal(b []byte, m protoreflect.Message) (out protoifac
 		out.Buf, err = o.marshalMessageSlow(b, m)
 	}
 	if err != nil {
+		var mismatch *protoerrors.SizeMismatchError
+		if errors.As(err, &mismatch) {
+			return out, fmt.Errorf("marshaling %s: %v", string(m.Descriptor().FullName()), err)
+		}
 		return out, err
 	}
 	if allowPartial {
diff --git a/proto/messageset.go b/proto/messageset.go
index 312d5d45c..575d14831 100644
--- a/proto/messageset.go
+++ b/proto/messageset.go
@@ -47,11 +47,16 @@ func (o MarshalOptions) marshalMessageSet(b []byte, m protoreflect.Message) ([]b
 func (o MarshalOptions) marshalMessageSetField(b []byte, fd protoreflect.FieldDescriptor, value protoreflect.Value) ([]byte, error) {
 	b = messageset.AppendFieldStart(b, fd.Number())
 	b = protowire.AppendTag(b, messageset.FieldMessage, protowire.BytesType)
-	b = protowire.AppendVarint(b, uint64(o.Size(value.Message().Interface())))
+	calculatedSize := o.Size(value.Message().Interface())
+	b = protowire.AppendVarint(b, uint64(calculatedSize))
+	before := len(b)
 	b, err := o.marshalMessage(b, value.Message())
 	if err != nil {
 		return b, err
 	}
+	if measuredSize := len(b) - before; calculatedSize != measuredSize {
+		return nil, errors.MismatchedSizeCalculation(calculatedSize, measuredSize)
+	}
 	b = messageset.AppendFieldEnd(b)
 	return b, nil
 }