diff --git a/codec.go b/codec.go
index 568c56ba..5d3f19b3 100644
--- a/codec.go
+++ b/codec.go
@@ -22,8 +22,9 @@ import (
 )
 
 const (
-	codecNameProto = "proto"
-	codecNameJSON  = "json"
+	codecNameProto           = "proto"
+	codecNameJSON            = "json"
+	codecNameJSONCharsetUTF8 = codecNameJSON + "; charset=utf-8"
 )
 
 // Codec marshals structs (typically generated from a schema) to and from bytes.
@@ -70,11 +71,13 @@ func (c *protoBinaryCodec) Unmarshal(data []byte, message any) error {
 	return proto.Unmarshal(data, protoMessage)
 }
 
-type protoJSONCodec struct{}
+type protoJSONCodec struct {
+	name string
+}
 
 var _ Codec = (*protoJSONCodec)(nil)
 
-func (c *protoJSONCodec) Name() string { return codecNameJSON }
+func (c *protoJSONCodec) Name() string { return c.name }
 
 func (c *protoJSONCodec) Marshal(message any) ([]byte, error) {
 	protoMessage, ok := message.(proto.Message)
diff --git a/error_writer.go b/error_writer.go
index efca9da1..1c62760f 100644
--- a/error_writer.go
+++ b/error_writer.go
@@ -83,7 +83,7 @@ func NewErrorWriter(opts ...HandlerOption) *ErrorWriter {
 // IsSupported checks whether a request is using one of the ErrorWriter's
 // supported RPC protocols.
 func (w *ErrorWriter) IsSupported(request *http.Request) bool {
-	ctype := request.Header.Get(headerContentType)
+	ctype := canonicalizeContentType(request.Header.Get(headerContentType))
 	_, ok := w.allContentTypes[ctype]
 	return ok
 }
@@ -94,7 +94,7 @@ func (w *ErrorWriter) IsSupported(request *http.Request) bool {
 //
 // Write does not read or close the request body.
 func (w *ErrorWriter) Write(response http.ResponseWriter, request *http.Request, err error) error {
-	ctype := request.Header.Get(headerContentType)
+	ctype := canonicalizeContentType(request.Header.Get(headerContentType))
 	if _, ok := w.unaryConnectContentTypes[ctype]; ok {
 		// Unary errors are always JSON.
 		response.Header().Set(headerContentType, connectUnaryContentTypeJSON)
diff --git a/handler.go b/handler.go
index 14950a22..86eda1b8 100644
--- a/handler.go
+++ b/handler.go
@@ -172,7 +172,7 @@ func (h *Handler) ServeHTTP(responseWriter http.ResponseWriter, request *http.Re
 	}
 
 	// Find our implementation of the RPC protocol in use.
-	contentType := request.Header.Get("Content-Type")
+	contentType := canonicalizeContentType(request.Header.Get("Content-Type"))
 	var protocolHandler protocolHandler
 	for _, handler := range h.protocolHandlers {
 		if _, ok := handler.ContentTypes()[contentType]; ok {
@@ -187,6 +187,7 @@ func (h *Handler) ServeHTTP(responseWriter http.ResponseWriter, request *http.Re
 	}
 
 	// Establish a stream and serve the RPC.
+	request.Header.Set("Content-Type", contentType) // prefer canonicalized value
 	ctx, cancel, timeoutErr := protocolHandler.SetTimeout(request)
 	if timeoutErr != nil {
 		ctx = request.Context()
@@ -235,7 +236,7 @@ func newHandlerConfig(procedure string, options []HandlerOption) *handlerConfig
 		BufferPool:       newBufferPool(),
 	}
 	withProtoBinaryCodec().applyToHandler(&config)
-	withProtoJSONCodec().applyToHandler(&config)
+	withProtoJSONCodecs().applyToHandler(&config)
 	withGzip().applyToHandler(&config)
 	for _, opt := range options {
 		opt.applyToHandler(&config)
diff --git a/handler_ext_test.go b/handler_ext_test.go
index e36da1a8..7135842c 100644
--- a/handler_ext_test.go
+++ b/handler_ext_test.go
@@ -74,15 +74,50 @@ func TestHandler_ServeHTTP(t *testing.T) {
 		assert.Equal(t, resp.Header.Get("Accept-Post"), strings.Join([]string{
 			"application/grpc",
 			"application/grpc+json",
+			"application/grpc+json; charset=utf-8",
 			"application/grpc+proto",
 			"application/grpc-web",
 			"application/grpc-web+json",
+			"application/grpc-web+json; charset=utf-8",
 			"application/grpc-web+proto",
 			"application/json",
+			"application/json; charset=utf-8",
 			"application/proto",
 		}, ", "))
 	})
 
+	t.Run("charset_in_content_type_header", func(t *testing.T) {
+		t.Parallel()
+		req, err := http.NewRequestWithContext(
+			context.Background(),
+			http.MethodPost,
+			server.URL+pingProcedure,
+			strings.NewReader("{}"),
+		)
+		assert.Nil(t, err)
+		req.Header.Set("Content-Type", "application/json;Charset=utf-8")
+		resp, err := client.Do(req)
+		assert.Nil(t, err)
+		defer resp.Body.Close()
+		assert.Equal(t, resp.StatusCode, http.StatusOK)
+	})
+
+	t.Run("unsupported_charset", func(t *testing.T) {
+		t.Parallel()
+		req, err := http.NewRequestWithContext(
+			context.Background(),
+			http.MethodPost,
+			server.URL+pingProcedure,
+			strings.NewReader("{}"),
+		)
+		assert.Nil(t, err)
+		req.Header.Set("Content-Type", "application/json; charset=shift-jis")
+		resp, err := client.Do(req)
+		assert.Nil(t, err)
+		defer resp.Body.Close()
+		assert.Equal(t, resp.StatusCode, http.StatusUnsupportedMediaType)
+	})
+
 	t.Run("unsupported_content_encoding", func(t *testing.T) {
 		t.Parallel()
 		req, err := http.NewRequestWithContext(
diff --git a/option.go b/option.go
index 9697245c..f86d75fe 100644
--- a/option.go
+++ b/option.go
@@ -78,7 +78,7 @@ func WithGRPCWeb() ClientOption {
 // lowerCamelCase, zero values are omitted, missing required fields are errors,
 // enums are emitted as strings, etc.
 func WithProtoJSON() ClientOption {
-	return WithCodec(&protoJSONCodec{})
+	return WithCodec(&protoJSONCodec{codecNameJSON})
 }
 
 // WithSendCompression configures the client to use the specified algorithm to
@@ -452,6 +452,9 @@ func withProtoBinaryCodec() Option {
 	return WithCodec(&protoBinaryCodec{})
 }
 
-func withProtoJSONCodec() HandlerOption {
-	return WithCodec(&protoJSONCodec{})
+func withProtoJSONCodecs() HandlerOption {
+	return WithHandlerOptions(
+		WithCodec(&protoJSONCodec{codecNameJSON}),
+		WithCodec(&protoJSONCodec{codecNameJSONCharsetUTF8}),
+	)
 }
diff --git a/protocol.go b/protocol.go
index 9f0cb8bc..e4b9f416 100644
--- a/protocol.go
+++ b/protocol.go
@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"mime"
 	"net/http"
 	"net/url"
 	"sort"
@@ -290,3 +291,11 @@ func flushResponseWriter(w http.ResponseWriter) {
 		f.Flush()
 	}
 }
+
+func canonicalizeContentType(ct string) string {
+	base, params, err := mime.ParseMediaType(ct)
+	if err != nil {
+		return ct
+	}
+	return mime.FormatMediaType(base, params)
+}