diff --git a/cardano-testnet/src/Testnet/Defaults.hs b/cardano-testnet/src/Testnet/Defaults.hs
index 32029b6333c..7e66c0d8d0b 100644
--- a/cardano-testnet/src/Testnet/Defaults.hs
+++ b/cardano-testnet/src/Testnet/Defaults.hs
@@ -32,8 +32,8 @@ module Testnet.Defaults
   , plutusV3Script
   ) where
 
-import           Cardano.Api (CardanoEra (..), File (..), pshow, ShelleyBasedEra (..),
-                   toCardanoEra, unsafeBoundedRational, AnyShelleyBasedEra (..))
+import           Cardano.Api (AnyShelleyBasedEra (..), CardanoEra (..), File (..),
+                   ShelleyBasedEra (..), pshow, toCardanoEra, unsafeBoundedRational)
 import qualified Cardano.Api.Shelley as Api
 
 import           Cardano.Ledger.Alonzo.Core (PParams (..))
@@ -433,7 +433,7 @@ defaultShelleyGenesis asbe startTime maxSupply options = do
       activeSlotsCoeff = round (shelleyActiveSlotsCoeff * 100) % 100
       -- make security param k satisfy: epochLength = 10 * k / f
       -- TODO: find out why this actually degrates network stability - turned off for now
-      -- securityParam = ceiling $ fromIntegral epochLength * cardanoActiveSlotsCoeff / 10
+      securityParam = ceiling $ fromIntegral epochLength * shelleyActiveSlotsCoeff / 10
       pVer = eraToProtocolVersion asbe
       protocolParams = Api.sgProtocolParams Api.shelleyGenesisDefaults
       protocolParamsWithPVer = protocolParams & ppProtocolVersionL' .~ pVer
@@ -444,7 +444,7 @@ defaultShelleyGenesis asbe startTime maxSupply options = do
         , Api.sgNetworkMagic = fromIntegral magic
         , Api.sgProtocolParams = protocolParamsWithPVer
         -- using default from shelley genesis k = 2160
-        -- , Api.sgSecurityParam = securityParam
+        , Api.sgSecurityParam = securityParam
         , Api.sgSlotLength = secondsToNominalDiffTimeMicro $ realToFrac slotLength
         , Api.sgSystemStart = startTime
         }
diff --git a/cardano-testnet/src/Testnet/Start/Types.hs b/cardano-testnet/src/Testnet/Start/Types.hs
index 7ab6af6a5e7..4f4817daff1 100644
--- a/cardano-testnet/src/Testnet/Start/Types.hs
+++ b/cardano-testnet/src/Testnet/Start/Types.hs
@@ -87,9 +87,9 @@ data ShelleyTestnetOptions = ShelleyTestnetOptions
 instance Default ShelleyTestnetOptions where
   def = ShelleyTestnetOptions
     { shelleyTestnetMagic = 42
-    , shelleyEpochLength = 500
-    , shelleySlotLength = 0.1
-    , shelleyActiveSlotsCoeff = 0.05
+    , shelleyEpochLength = 150_000
+    , shelleySlotLength = 0.15
+    , shelleyActiveSlotsCoeff = 0.1
     }
 
 -- | Specify a BFT node (Pre-Babbage era only) or an SPO (Shelley era onwards only)