diff --git a/src/RNTuple/Writing/constants.jl b/src/RNTuple/Writing/constants.jl
index 18a61200..fbb13012 100644
--- a/src/RNTuple/Writing/constants.jl
+++ b/src/RNTuple/Writing/constants.jl
@@ -9,6 +9,7 @@ const RNTUPLE_WRITE_TYPE_IDX_DICT = Dict(
     UInt64 => (0x0A, sizeof(UInt64) * 8),
     UInt32 => (0x0B, sizeof(UInt32) * 8),
     UInt16 => (0x0C, sizeof(UInt16) * 8),
+    UInt8 => (0x0D, sizeof(UInt8) * 8),
     Int64 => (0x16, sizeof(Int64) * 8),
     Int32 => (0x17, sizeof(Int32) * 8),
     Int16 => (0x18, sizeof(Int16) * 8),
@@ -24,6 +25,7 @@ const RNTUPLE_WRITE_TYPE_CPPNAME_DICT = Dict(
     Int16 => "std::int16_t",
     Int32 => "std::int32_t",
     Int64 => "std::int64_t",
+    UInt8 => "std::uint8_t",
     UInt16 => "std::uint16_t",
     UInt32 => "std::uint32_t",
     UInt64 => "std::uint64_t",