diff --git a/lib/core/src/Cardano/Wallet/Primitive/Types.hs b/lib/core/src/Cardano/Wallet/Primitive/Types.hs
index b32e6eeb9d6..cd61218080e 100644
--- a/lib/core/src/Cardano/Wallet/Primitive/Types.hs
+++ b/lib/core/src/Cardano/Wallet/Primitive/Types.hs
@@ -96,6 +96,7 @@ module Cardano.Wallet.Primitive.Types
     , EpochNo (..)
     , FeePolicy (..)
     , SlotId (..)
+    , SlotInternalIndex (..)
     , SlotLength (..)
     , SlotNo (..)
     , StartTime (..)
@@ -1807,6 +1808,17 @@ newtype StartTime = StartTime UTCTime
 
 instance NFData StartTime
 
+-- | Indicates the relative position of an event occurring within a slot.
+--
+-- If 'SlotInternalIndex' values @a@ and @b@ correspond to the same slot, then:
+--
+--   * @a > b@ indicates that @a@ occurs later than @b@.
+--   * @a < b@ indicates that @b@ occurs later than @a@.
+--   * @a = b@ indicates that @a@ and @b@ occur at the same point.
+--
+newtype SlotInternalIndex = SlotInternalIndex { unSlotInternalIndex :: Word64 }
+    deriving (Bounded, Enum, Eq, Ord, Show, Read)
+
 {-------------------------------------------------------------------------------
                                 Protocol Magic
 -------------------------------------------------------------------------------}