diff --git a/compiler/src/prog8/compiler/astprocessing/LiteralsToAutoVars.kt b/compiler/src/prog8/compiler/astprocessing/LiteralsToAutoVars.kt
index 326e80d9f..82a4c0970 100644
--- a/compiler/src/prog8/compiler/astprocessing/LiteralsToAutoVars.kt
+++ b/compiler/src/prog8/compiler/astprocessing/LiteralsToAutoVars.kt
@@ -49,6 +49,8 @@ internal class LiteralsToAutoVars(private val program: Program, private val erro
             }
         } else {
             val arrayDt = array.guessDatatype(program)
+            if(arrayDt.isUnknown)
+                return noModifications
             val elementDt = ArrayToElementTypes.getValue(arrayDt.getOr(DataType.UNDEFINED))
             val maxSize = when(elementDt) {
                 in ByteDatatypesWithBoolean -> PtContainmentCheck.MAX_SIZE_FOR_INLINE_CHECKS_BYTE