diff --git a/examples/req/Main.hs b/examples/req/Main.hs
--- a/examples/req/Main.hs
+++ b/examples/req/Main.hs
@@ -3,7 +3,7 @@
 import Control.Concurrent
 import Data.Maybe
 import LightStep.HighLevel.IO
-import LightStep.Propagation (headersForSpanContext)
+import LightStep.Propagation (b3headersForSpanContext)
 import Network.HTTP.Req
 import qualified Data.Text as T
 import System.Environment
@@ -15,7 +15,7 @@
     setTag "span.kind" "client"
     setTag "component" "http"
     Just ctx <- currentSpanContext
-    let opts = port 8736 <> foldMap (\(k, v) -> header k v) (headersForSpanContext ctx)
+    let opts = port 8736 <> foldMap (\(k, v) -> header k v) (b3headersForSpanContext ctx)
         url = http "127.0.0.1" /: "test"
     runReq defaultHttpConfig $ req GET url NoReqBody ignoreResponse opts
   threadDelay 1_000_000
diff --git a/lightstep-haskell.cabal b/lightstep-haskell.cabal
--- a/lightstep-haskell.cabal
+++ b/lightstep-haskell.cabal
@@ -1,7 +1,7 @@
 cabal-version: 2.4
 
 name:           lightstep-haskell
-version:        0.4.2
+version:        0.4.3
 synopsis:       LightStep OpenTracing client library
 description:    LightStep OpenTracing client library. Uses GRPC transport via proto-lens.
 category:       Tools
diff --git a/src/LightStep/Propagation.hs b/src/LightStep/Propagation.hs
--- a/src/LightStep/Propagation.hs
+++ b/src/LightStep/Propagation.hs
@@ -1,17 +1,17 @@
-{-# language OverloadedStrings #-}
+{-# LANGUAGE OverloadedStrings #-}
 
 module LightStep.Propagation where
 
-import Data.Bits
 import Control.Lens
-import Data.List (foldl')
+import Data.Bits
 import qualified Data.ByteString as BS
+import Data.List (foldl')
 import Data.ProtoLens.Message (defMessage)
+import GHC.Word
 import Network.HTTP.Types
 import Network.Wai
 import Proto.Collector
 import Proto.Collector_Fields
-import GHC.Word
 
 extractSpanContextFromRequest :: Request -> Maybe SpanContext
 extractSpanContextFromRequest = extractSpanContextFromRequestHeaders . requestHeaders
@@ -19,32 +19,38 @@
 extractSpanContextFromRequestHeaders :: RequestHeaders -> Maybe SpanContext
 extractSpanContextFromRequestHeaders hdrs =
   case foldl' go (Nothing, Nothing) hdrs of
-    (Just tid, Just sid) -> defMessage
-      & traceId .~ tid
-      & spanId .~ sid
-      & Just
+    (Just tid, Just sid) ->
+      defMessage
+        & traceId .~ tid
+        & spanId .~ sid
+        & Just
     _ -> Nothing
   where
-  -- TODO: Zipkin style propagation
-
-  go (_, sid) ("ot-tracer-traceid", decode_u64 -> Just tid) = (Just tid, sid)
-  go (tid, _) ("ot-tracer-spanid", decode_u64 -> Just sid) = (tid, Just sid)
-
-  -- TODO: Propagation of the whole span context in a single header
-  -- go _ ("x-ot-span-context", parse128 -> Just (tid, sid)) = (Just tid, Just sid)
-
-  go acc _ = acc
+    -- TODO: 128-bit x-b3-traceid
+    go (_, sid) ("x-b3-traceid", decode_u64 -> Just tid) = (Just tid, sid)
+    go (tid, _) ("x-b3-spanid", decode_u64 -> Just sid) = (tid, Just sid)
+    go (_, sid) ("ot-tracer-traceid", decode_u64 -> Just tid) = (Just tid, sid)
+    go (tid, _) ("ot-tracer-spanid", decode_u64 -> Just sid) = (tid, Just sid)
+    -- TODO: Propagation of the whole span context in a single header
+    -- go _ ("x-ot-span-context", parse128 -> Just (tid, sid)) = (Just tid, Just sid)
 
+    go acc _ = acc
 
-  -- parse128 :: BS.ByteString -> Maybe (Word64, Word64)
-  -- parse128 _ = Nothing -- TODO
+-- parse128 :: BS.ByteString -> Maybe (Word64, Word64)
+-- parse128 _ = Nothing -- TODO
 
 headersForSpanContext :: SpanContext -> [(BS.ByteString, BS.ByteString)]
 headersForSpanContext ctx =
-  [ ("ot-tracer-traceid", encode_u64 $ ctx ^. traceId)
-  , ("ot-tracer-spanid", encode_u64 $ ctx ^. spanId)
+  [ ("ot-tracer-traceid", encode_u64 $ ctx ^. traceId),
+    ("ot-tracer-spanid", encode_u64 $ ctx ^. spanId)
   ]
 
+b3headersForSpanContext :: SpanContext -> [(BS.ByteString, BS.ByteString)]
+b3headersForSpanContext ctx =
+  [ ("x-b3-traceid", encode_u64 $ ctx ^. traceId),
+    ("x-b3-spanid", encode_u64 $ ctx ^. spanId)
+  ]
+
 encode_u64 :: Word64 -> BS.ByteString
 -- TODO: a better way to encode base16
 encode_u64 x =
@@ -55,14 +61,13 @@
       go :: Int -> [Word8] -> Word64 -> [Word8]
       go 0 acc _ = acc
       go n acc v = go (n - 1) (encodeChar (fromIntegral v .&. 0x0f) : acc) (v `div` 16)
-  in BS.pack hexDigits
+   in BS.pack hexDigits
 
 decode_u64 :: BS.ByteString -> Maybe Word64
 decode_u64 bytes | BS.length bytes /= 16 = Nothing
 decode_u64 bytes = BS.foldl' go (Just 0) bytes
   where
-  go Nothing _ = Nothing
-  go (Just !result) d | d >= 48 && d < 58 = Just $ result * 16 + fromIntegral d - 48
-  go (Just result) d | d >= 97 && d < 124 = Just $ result * 16 + fromIntegral d - 87
-  go _ _ = Nothing
-
+    go Nothing _ = Nothing
+    go (Just !result) d | d >= 48 && d < 58 = Just $ result * 16 + fromIntegral d - 48
+    go (Just result) d | d >= 97 && d < 124 = Just $ result * 16 + fromIntegral d - 87
+    go _ _ = Nothing