diff --git a/.changes/20260827_121029_cardano-cli_palas_dijkstra_simple_scripts.yml b/.changes/20260827_121029_cardano-cli_palas_dijkstra_simple_scripts.yml
new file mode 100644
index 0000000000..f6ce790194
--- /dev/null
+++ b/.changes/20260827_121029_cardano-cli_palas_dijkstra_simple_scripts.yml
@@ -0,0 +1,6 @@
+description: |
+  Simple scripts read from JSON files now work in the Dijkstra era, instead of aborting with an internal TODO error.
+kind:
+- feature
+pr: 1427
+project: cardano-cli
diff --git a/cardano-cli/src/Cardano/CLI/EraBased/Script/Read/Common.hs b/cardano-cli/src/Cardano/CLI/EraBased/Script/Read/Common.hs
index 7c3254ad8c..c150f9a7d9 100644
--- a/cardano-cli/src/Cardano/CLI/EraBased/Script/Read/Common.hs
+++ b/cardano-cli/src/Cardano/CLI/EraBased/Script/Read/Common.hs
@@ -21,6 +21,7 @@ import Cardano.CLI.Read (readFileCli)
 import Cardano.CLI.Type.Common
 import Cardano.CLI.Type.Error.ScriptDataError
 import Cardano.Ledger.Core qualified as L
+import Cardano.Ledger.Dijkstra.Scripts qualified as Dijkstra
 
 import Prelude
 
@@ -38,14 +39,16 @@ readFileSimpleScript
 readFileSimpleScript file era = do
   bs <- readFileCli file
   case deserialiseFromJSON bs of
-    Left _ -> case era of
-      Exp.DijkstraEra -> error "TODO Dijkstra: Simple script not supported"
-      Exp.ConwayEra -> Exp.obtainConwayConstraints era $ do
-        -- In addition to the TextEnvelope format, we also try to
-        -- deserialize the JSON representation of SimpleScripts..
-        script :: SimpleScript <- fromEitherCli $ Aeson.eitherDecodeStrict' bs
-        let s :: L.NativeScript (Exp.LedgerEra era) = obtainCommonConstraints era $ toAllegraTimelock script
-        return $ Exp.SimpleScript s
+    Left _ -> do
+      -- In addition to the TextEnvelope format, we also try to
+      -- deserialize the JSON representation of SimpleScripts.
+      script :: SimpleScript <- fromEitherCli $ Aeson.eitherDecodeStrict' bs
+      let conwayTimelock :: L.NativeScript (Exp.LedgerEra Exp.ConwayEra)
+          conwayTimelock = toAllegraTimelock script
+      Exp.obtainCommonConstraints era $
+        pure . Exp.SimpleScript $ case era of
+          Exp.DijkstraEra -> Dijkstra.upgradeTimelock conwayTimelock
+          Exp.ConwayEra -> conwayTimelock
     Right te -> do
       let scriptBs = teRawCBOR te
       obtainCommonConstraints era $