diff --git a/examples/internal/integration/integration_test.go b/examples/internal/integration/integration_test.go
index 3382b9483d1..954d2f040bc 100644
--- a/examples/internal/integration/integration_test.go
+++ b/examples/internal/integration/integration_test.go
@@ -53,6 +53,8 @@ func TestEcho(t *testing.T) {
 			testEchoBody(t, 8089, apiPrefix, true)
 			testEchoBody(t, 8089, apiPrefix, false)
 			testEchoBodyParamOverwrite(t, 8088)
+			testEchoWithNonASCIIHeaderValues(t, 8088, apiPrefix)
+			testEchoWithInvalidHeaderKey(t, 8088, apiPrefix)
 		})
 	}
 }
@@ -2504,3 +2506,79 @@ func testABETrace(t *testing.T, port int) {
 		return
 	}
 }
+
+func testEchoWithNonASCIIHeaderValues(t *testing.T, port int, apiPrefix string) {
+	apiURL := fmt.Sprintf("http://localhost:%d/%s/example/echo/myid", port, apiPrefix)
+
+	req, err := http.NewRequest("POST", apiURL, strings.NewReader("{}"))
+	if err != nil {
+		t.Errorf("http.NewRequest() = err: %v", err)
+		return
+	}
+	req.Header.Add("Content-Type", "application/json")
+	req.Header.Add("Grpc-Metadata-Location", "Gjøvik")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Errorf("http.Post(%q) failed with %v; want success", apiURL, err)
+		return
+	}
+	defer resp.Body.Close()
+
+	buf, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Errorf("io.ReadAll(resp.Body) failed with %v; want success", err)
+		return
+	}
+
+	if got, want := resp.StatusCode, http.StatusOK; got != want {
+		t.Errorf("resp.StatusCode = %d; want %d", got, want)
+		t.Logf("%s", buf)
+	}
+
+	msg := new(examplepb.UnannotatedSimpleMessage)
+	if err := marshaler.Unmarshal(buf, msg); err != nil {
+		t.Errorf("marshaler.Unmarshal(%s, msg) failed with %v; want success", buf, err)
+		return
+	}
+	if got, want := msg.Id, "myid"; got != want {
+		t.Errorf("msg.Id = %q; want %q", got, want)
+	}
+}
+
+func testEchoWithInvalidHeaderKey(t *testing.T, port int, apiPrefix string) {
+	apiURL := fmt.Sprintf("http://localhost:%d/%s/example/echo/myid", port, apiPrefix)
+
+	req, err := http.NewRequest("POST", apiURL, strings.NewReader("{}"))
+	if err != nil {
+		t.Errorf("http.NewRequest() = err: %v", err)
+		return
+	}
+	req.Header.Add("Content-Type", "application/json")
+	req.Header.Add("Grpc-Metadata-Foo+Bar", "Hello")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Errorf("http.Post(%q) failed with %v; want success", apiURL, err)
+		return
+	}
+	defer resp.Body.Close()
+
+	buf, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Errorf("io.ReadAll(resp.Body) failed with %v; want success", err)
+		return
+	}
+
+	if got, want := resp.StatusCode, http.StatusOK; got != want {
+		t.Errorf("resp.StatusCode = %d; want %d", got, want)
+		t.Logf("%s", buf)
+	}
+
+	msg := new(examplepb.UnannotatedSimpleMessage)
+	if err := marshaler.Unmarshal(buf, msg); err != nil {
+		t.Errorf("marshaler.Unmarshal(%s, msg) failed with %v; want success", buf, err)
+		return
+	}
+	if got, want := msg.Id, "myid"; got != want {
+		t.Errorf("msg.Id = %q; want %q", got, want)
+	}
+}
diff --git a/runtime/BUILD.bazel b/runtime/BUILD.bazel
index b5140a3c9d1..195df460c39 100644
--- a/runtime/BUILD.bazel
+++ b/runtime/BUILD.bazel
@@ -26,6 +26,7 @@ go_library(
     deps = [
         "//internal/httprule",
         "//utilities",
+        "@com_github_golang_glog//:glog",
         "@go_googleapis//google/api:httpbody_go_proto",
         "@io_bazel_rules_go//proto/wkt:field_mask_go_proto",
         "@org_golang_google_grpc//codes",
diff --git a/runtime/context.go b/runtime/context.go
index 5ab5b3841da..9956e7ef0bd 100644
--- a/runtime/context.go
+++ b/runtime/context.go
@@ -12,6 +12,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/golang/glog"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
@@ -99,6 +100,38 @@ func AnnotateIncomingContext(ctx context.Context, mux *ServeMux, req *http.Reque
 	return metadata.NewIncomingContext(ctx, md), nil
 }
 
+func isValidGRPCMetadataKey(key string) bool {
+	// Must be a valid gRPC "Header-Name" as defined here:
+	//   https://github.com/grpc/grpc/blob/4b05dc88b724214d0c725c8e7442cbc7a61b1374/doc/PROTOCOL-HTTP2.md
+	// This means 0-9 a-z _ - .
+	// Only lowercase letters are valid in the wire protocol, but the client library will normalize
+	// uppercase ASCII to lowercase, so uppercase ASCII is also acceptable.
+	bytes := []byte(key) // gRPC validates strings on the byte level, not Unicode.
+	for _, ch := range bytes {
+		validLowercaseLetter := ch >= 'a' && ch <= 'z'
+		validUppercaseLetter := ch >= 'A' && ch <= 'Z'
+		validDigit := ch >= '0' && ch <= '9'
+		validOther := ch == '.' || ch == '-' || ch == '_'
+		if !validLowercaseLetter && !validUppercaseLetter && !validDigit && !validOther {
+			return false
+		}
+	}
+	return true
+}
+
+func isValidGRPCMetadataTextValue(textValue string) bool {
+	// Must be a valid gRPC "ASCII-Value" as defined here:
+	//   https://github.com/grpc/grpc/blob/4b05dc88b724214d0c725c8e7442cbc7a61b1374/doc/PROTOCOL-HTTP2.md
+	// This means printable ASCII (including/plus spaces); 0x20 to 0x7E inclusive.
+	bytes := []byte(textValue) // gRPC validates strings on the byte level, not Unicode.
+	for _, ch := range bytes {
+		if ch < 0x20 || ch > 0x7E {
+			return false
+		}
+	}
+	return true
+}
+
 func annotateContext(ctx context.Context, mux *ServeMux, req *http.Request, rpcMethodName string, options ...AnnotateContextOption) (context.Context, metadata.MD, error) {
 	ctx = withRPCMethod(ctx, rpcMethodName)
 	for _, o := range options {
@@ -121,6 +154,10 @@ func annotateContext(ctx context.Context, mux *ServeMux, req *http.Request, rpcM
 				pairs = append(pairs, "authorization", val)
 			}
 			if h, ok := mux.incomingHeaderMatcher(key); ok {
+				if !isValidGRPCMetadataKey(h) {
+					glog.Errorf("HTTP header name %q is not valid as gRPC metadata key; skipping", h)
+					continue
+				}
 				// Handles "-bin" metadata in grpc, since grpc will do another base64
 				// encode before sending to server, we need to decode it first.
 				if strings.HasSuffix(key, metadataHeaderBinarySuffix) {
@@ -130,6 +167,9 @@ func annotateContext(ctx context.Context, mux *ServeMux, req *http.Request, rpcM
 					}
 
 					val = string(b)
+				} else if !isValidGRPCMetadataTextValue(val) {
+					glog.Errorf("Value of HTTP header %q contains non-ASCII value (not valid as gRPC metadata): skipping", h)
+					continue
 				}
 				pairs = append(pairs, h, val)
 			}