diff --git a/src/Juvix/Compiler/Casm/Translation/FromReg.hs b/src/Juvix/Compiler/Casm/Translation/FromReg.hs
index 51caa02a7c..1cac6232ed 100644
--- a/src/Juvix/Compiler/Casm/Translation/FromReg.hs
+++ b/src/Juvix/Compiler/Casm/Translation/FromReg.hs
@@ -249,7 +249,7 @@ fromReg tab = mkResult $ run $ runLabelInfoBuilderWithNextId (Reg.getNextSymbolI
           Reg.ConstUnit -> 0
           Reg.ConstVoid -> 0
           Reg.ConstString {} -> unsupported "strings"
-          Reg.ConstUInt8 x -> toInteger x
+          Reg.ConstUInt8 {} -> unsupported "uint8"
 
         mkLoad :: Reg.ConstrField -> Sem r RValue
         mkLoad Reg.ConstrField {..} = do
@@ -459,8 +459,8 @@ fromReg tab = mkResult $ run $ runLabelInfoBuilderWithNextId (Reg.getNextSymbolI
           Reg.OpFieldToInt -> goAssignValue _instrUnopResult _instrUnopArg
           Reg.OpIntToField -> goAssignValue _instrUnopResult _instrUnopArg
           Reg.OpArgsNum -> goUnop' goOpArgsNum _instrUnopResult _instrUnopArg
-          Reg.OpUInt8ToInt -> goAssignValue _instrUnopResult _instrUnopArg
-          Reg.OpIntToUInt8 -> unsupported "OpIntTOUInt8"
+          Reg.OpUInt8ToInt -> unsupported "OpUInt8ToInt"
+          Reg.OpIntToUInt8 -> unsupported "OpIntToUInt8"
 
         goCairo :: Reg.InstrCairo -> Sem r ()
         goCairo Reg.InstrCairo {..} = case _instrCairoOpcode of
diff --git a/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs b/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs
index daabb5b6a9..8b7b3fb7e9 100644
--- a/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs
+++ b/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs
@@ -12,7 +12,7 @@ checkCairo md = do
   checkMainType
   checkNoAxioms md
   mapAllNodesM checkNoIO md
-  mapAllNodesM (checkBuiltins' builtinsString [PrimString, primitiveUInt8]) md
+  mapAllNodesM (checkBuiltins' (builtinsString ++ builtinsUInt8) [PrimString, primitiveUInt8]) md
   where
     checkMainType :: Sem r ()
     checkMainType =