diff --git a/internal/fuzz/wirefuzz/fuzz.go b/internal/fuzz/wirefuzz/fuzz.go
index 0c08466..f7a9b74 100644
--- a/internal/fuzz/wirefuzz/fuzz.go
+++ b/internal/fuzz/wirefuzz/fuzz.go
@@ -10,6 +10,7 @@
 
 	"google.golang.org/protobuf/internal/impl"
 	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protoregistry"
 	piface "google.golang.org/protobuf/runtime/protoiface"
 
 	fuzzpb "google.golang.org/protobuf/internal/testprotos/fuzz"
@@ -17,14 +18,11 @@
 
 // Fuzz is a fuzzer for proto.Marshal and proto.Unmarshal.
 func Fuzz(data []byte) (score int) {
+	// Unmarshal and Validate should agree about the validity of the message.
 	m1 := &fuzzpb.Fuzz{}
-	vout, valid := impl.Validate(m1.ProtoReflect().Type(), piface.UnmarshalInput{
-		Buf: data,
-	})
-	vinit := vout.Flags&piface.UnmarshalInitialized != 0
-	if err := (proto.UnmarshalOptions{
-		AllowPartial: true,
-	}).Unmarshal(data, m1); err != nil {
+	mt := m1.ProtoReflect().Type()
+	_, valid := impl.Validate(mt, piface.UnmarshalInput{Buf: data})
+	if err := (proto.UnmarshalOptions{AllowPartial: true}).Unmarshal(data, m1); err != nil {
 		switch valid {
 		case impl.ValidationUnknown:
 		case impl.ValidationInvalid:
@@ -39,22 +37,46 @@
 	default:
 		panic("unmarshal ok with validation status: " + valid.String())
 	}
-	if proto.CheckInitialized(m1) != nil && vinit {
-		panic("validation reports partial message is initialized")
+
+	// Unmarshal, Validate, and CheckInitialized should agree about initialization.
+	checkInit := proto.CheckInitialized(m1) == nil
+	methods := m1.ProtoReflect().ProtoMethods()
+	in := piface.UnmarshalInput{Message: mt.New(), Resolver: protoregistry.GlobalTypes}
+	if checkInit {
+		// If the message initialized, the both Unmarshal and Validate should
+		// report it as such. False negatives are tolerated, but have a
+		// significant impact on performance. In general, they should always
+		// properly determine initialization for any normalized message,
+		// we produce by re-marshaling the message.
+		in.Buf, _ = proto.Marshal(m1)
+		if out, _ := methods.Unmarshal(in); out.Flags&piface.UnmarshalInitialized == 0 {
+			panic("unmarshal reports initialized message as partial")
+		}
+		if out, _ := impl.Validate(mt, in); out.Flags&piface.UnmarshalInitialized == 0 {
+			panic("validate reports initialized message as partial")
+		}
+	} else {
+		// If the message is partial, then neither Unmarshal nor Validate
+		// should ever report it as such. False positives are unacceptable.
+		in.Buf = data
+		if out, _ := methods.Unmarshal(in); out.Flags&piface.UnmarshalInitialized != 0 {
+			panic("unmarshal reports partial message as initialized")
+		}
+		if out, _ := impl.Validate(mt, in); out.Flags&piface.UnmarshalInitialized != 0 {
+			panic("validate reports partial message as initialized")
+		}
 	}
-	data1, err := proto.MarshalOptions{
-		AllowPartial: true,
-	}.Marshal(m1)
+
+	// Round-trip Marshal and Unmarshal should produce the same messages.
+	data1, err := proto.MarshalOptions{AllowPartial: !checkInit}.Marshal(m1)
 	if err != nil {
 		panic(err)
 	}
 	if proto.Size(m1) != len(data1) {
-		panic(fmt.Errorf("size does not match output %v", m1))
+		panic(fmt.Errorf("size does not match output: %d != %d", proto.Size(m1), len(data1)))
 	}
 	m2 := &fuzzpb.Fuzz{}
-	if err := (proto.UnmarshalOptions{
-		AllowPartial: true,
-	}).Unmarshal(data1, m2); err != nil {
+	if err := (proto.UnmarshalOptions{AllowPartial: !checkInit}).Unmarshal(data1, m2); err != nil {
 		panic(err)
 	}
 	if !proto.Equal(m1, m2) {