diff --git a/transport/http_util.go b/transport/http_util.go
index f1233fa..2517311 100644
--- a/transport/http_util.go
+++ b/transport/http_util.go
@@ -120,7 +120,7 @@
 // reserved by gRPC protocol. Any other headers are classified as the
 // user-specified metadata.
 func isReservedHeader(hdr string) bool {
-	if hdr[0] == ':' {
+	if hdr != "" && hdr[0] == ':' {
 		return true
 	}
 	switch hdr {
diff --git a/transport/transport_test.go b/transport/transport_test.go
index 4b50f73..07128d5 100644
--- a/transport/transport_test.go
+++ b/transport/transport_test.go
@@ -660,3 +660,26 @@
 		t.Fatalf("GetStreamFromContext(%v) = %v, %t, want: %v, true", ctx, *s, ok, expectedStream)
 	}
 }
+
+func TestIsReservedHeader(t *testing.T) {
+	tests := []struct {
+		h    string
+		want bool
+	}{
+		{"", false}, // but should be rejected earlier
+		{"foo", false},
+		{"content-type", true},
+		{"grpc-message-type", true},
+		{"grpc-encoding", true},
+		{"grpc-message", true},
+		{"grpc-status", true},
+		{"grpc-timeout", true},
+		{"te", true},
+	}
+	for _, tt := range tests {
+		got := isReservedHeader(tt.h)
+		if got != tt.want {
+			t.Errorf("isReservedHeader(%q) = %v; want %v", tt.h, got, tt.want)
+		}
+	}
+}