diff --git a/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Protocol/Praos.hs b/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Protocol/Praos.hs
index 82c04938105..28e3d53c68f 100644
--- a/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Protocol/Praos.hs
+++ b/ouroboros-consensus/ouroboros-consensus-mock/src/Ouroboros/Consensus/Mock/Protocol/Praos.hs
@@ -46,6 +46,7 @@ import           Data.Proxy (Proxy (..))
 import           Data.Typeable
 import           Data.Word (Word64)
 import           GHC.Generics (Generic)
+import           GHC.Stack
 import           Numeric.Natural
 
 import           Cardano.Crypto.DSIGN.Ed448 (Ed448DSIGN)
@@ -141,18 +142,21 @@ forgePraosFields :: ( MonadRandom m
                  -> (PraosExtraFields c -> toSign)
                  -> m (PraosFields c toSign)
 forgePraosFields PraosNodeConfig{..} updateState PraosProof{..} mkToSign = do
-    keyKES <- runUpdate updateState $ \case
+    -- For the mock implementation, we consider the KES period to be the slot.
+    -- In reality, there will be some kind of constants slotsPerPeriod factor.
+    let kesPeriod :: Natural
+        kesPeriod = fromIntegral (unSlotNo praosProofSlot)
+
+    oldKey <- runUpdate updateState $ \case
       PraosKeyEvolving ->
         -- Another thread is currently evolving the key; wait
         Nothing
       PraosKeyAvailable oldKey ->
-        -- TODO : We should not update the key on each signing, but X slots
-        -- (for configurable param X)
         return (PraosKeyEvolving, oldKey)
 
-    -- Evolve the key (if needed)
+    -- Evolve the key
     newKey <- fromMaybe (error "mkOutoborosPayload: updateKES failed") <$>
-                 updateKES () keyKES
+                 updateKESTo () kesPeriod oldKey
     runUpdate updateState $ \_ -> return (PraosKeyAvailable newKey, ())
 
     let signedFields = PraosExtraFields {
@@ -160,19 +164,37 @@ forgePraosFields PraosNodeConfig{..} updateState PraosProof{..} mkToSign = do
         , praosRho     = praosProofRho
         , praosY       = praosProofY
         }
-    m <- signedKES
-           ()
-           (fromIntegral (unSlotNo praosProofSlot))
-           (mkToSign signedFields)
-           keyKES
+    m <- signedKES () kesPeriod (mkToSign signedFields) newKey
     case m of
       Nothing -> error "mkOutoborosPayload: signedKES failed"
       Just signature -> do
         return $ PraosFields {
-            praosSignature    = signature
+            praosSignature   = signature
           , praosExtraFields = signedFields
           }
 
+-- | Update key to specified period
+--
+-- Throws an error if the key is already /past/ the period
+updateKESTo :: forall m v. (MonadRandom m, HasCallStack, KESAlgorithm v)
+            => ContextKES v
+            -> Natural -- ^ KES period to evolve to
+            -> SignKeyKES v
+            -> m (Maybe (SignKeyKES v))
+updateKESTo ctxt evolveTo = go
+  where
+    go :: SignKeyKES v -> m (Maybe (SignKeyKES v))
+    go key
+      | iterationCountKES ctxt key < evolveTo = do
+          mKey' <- updateKES ctxt key
+          case mKey' of
+            Nothing   -> return Nothing
+            Just key' -> go key'
+      | iterationCountKES ctxt key == evolveTo =
+          return (Just key)
+      | otherwise =
+          error "updateKESTo: key already past period"
+
 {-------------------------------------------------------------------------------
   Praos specific types
 -------------------------------------------------------------------------------}
diff --git a/ouroboros-consensus/ouroboros-consensus-mock/test/Main.hs b/ouroboros-consensus/ouroboros-consensus-mock/test/Main.hs
index a4a0ffef2b0..0e0e2672c80 100644
--- a/ouroboros-consensus/ouroboros-consensus-mock/test/Main.hs
+++ b/ouroboros-consensus/ouroboros-consensus-mock/test/Main.hs
@@ -6,7 +6,7 @@ import qualified Test.Consensus.Ledger.Mock (tests)
 import qualified Test.ThreadNet.BFT (tests)
 import qualified Test.ThreadNet.LeaderSchedule (tests)
 import qualified Test.ThreadNet.PBFT (tests)
--- import qualified Test.ThreadNet.Praos (tests)
+import qualified Test.ThreadNet.Praos (tests)
 
 main :: IO ()
 main = defaultMain tests
@@ -18,5 +18,5 @@ tests =
   , Test.ThreadNet.BFT.tests
   , Test.ThreadNet.LeaderSchedule.tests
   , Test.ThreadNet.PBFT.tests
---  , Test.ThreadNet.Praos.tests
+  , Test.ThreadNet.Praos.tests
   ]