diff --git a/compiler/src/prog8/ast/expressions/AstExpressions.kt b/compiler/src/prog8/ast/expressions/AstExpressions.kt
index 470165321..24f4d85ed 100644
--- a/compiler/src/prog8/ast/expressions/AstExpressions.kt
+++ b/compiler/src/prog8/ast/expressions/AstExpressions.kt
@@ -497,7 +497,11 @@ class ReferenceLiteralValue(val type: DataType,     // only reference types allo
                                 throw FatalAstException("weird array element $it")
                             it
                         } else {
-                            num.cast(elementType)    // TODO this can throw an exception
+                            try {
+                                num.cast(elementType)
+                            } catch(x: ExpressionError) {
+                                return null
+                            }
                         }
                     }.toTypedArray()
                     return ReferenceLiteralValue(targettype, null, array=castArray, position = position)
@@ -668,7 +672,7 @@ data class IdentifierReference(val nameInSource: List<String>, override val posi
 
     override fun accept(visitor: IAstModifyingVisitor) = visitor.visit(this)
     override fun accept(visitor: IAstVisitor) = visitor.visit(this)
-    override fun referencesIdentifiers(vararg name: String): Boolean = nameInSource.last() in name   // @todo is this correct all the time?
+    override fun referencesIdentifiers(vararg name: String): Boolean = nameInSource.last() in name
 
     override fun inferType(program: Program): DataType? {
         val targetStmt = targetStatement(program.namespace)
diff --git a/compiler/src/prog8/ast/processing/AstIdentifiersChecker.kt b/compiler/src/prog8/ast/processing/AstIdentifiersChecker.kt
index 984f21f4f..b23b64d78 100644
--- a/compiler/src/prog8/ast/processing/AstIdentifiersChecker.kt
+++ b/compiler/src/prog8/ast/processing/AstIdentifiersChecker.kt
@@ -390,7 +390,7 @@ internal fun fixupArrayDatatype(array: ReferenceLiteralValue, vardecl: VarDecl,
                     }
             vardecl.value = litval2
             litval2.linkParents(vardecl)
-            litval2.addToHeap(heap)     // TODO is the previous array discarded from the resulting asm code?
+            litval2.addToHeap(heap)
             return litval2
         }
     } else {
diff --git a/compiler/src/prog8/compiler/Zeropage.kt b/compiler/src/prog8/compiler/Zeropage.kt
index 3aa5859cf..bb490799a 100644
--- a/compiler/src/prog8/compiler/Zeropage.kt
+++ b/compiler/src/prog8/compiler/Zeropage.kt
@@ -13,7 +13,7 @@ abstract class Zeropage(protected val options: CompilationOptions) {
 
     val allowedDatatypes = NumericDatatypes
 
-    fun available() = free.size
+    fun available() = if(options.zeropage==ZeropageType.DONTUSE) 0 else free.size
 
     fun allocate(scopedname: String, datatype: DataType, position: Position?): Int {
         assert(scopedname.isEmpty() || !allocations.values.any { it.first==scopedname } ) {"isSameAs scopedname can't be allocated twice"}
diff --git a/compiler/src/prog8/optimizer/ConstantFolding.kt b/compiler/src/prog8/optimizer/ConstantFolding.kt
index ed4016785..6be1bb7e3 100644
--- a/compiler/src/prog8/optimizer/ConstantFolding.kt
+++ b/compiler/src/prog8/optimizer/ConstantFolding.kt
@@ -210,7 +210,7 @@ class ConstantFolding(private val program: Program) : IAstModifyingVisitor {
                     val possibleDts = arg.second.possibleDatatypes
                     val argConst = arg.first.value.constValue(program)
                     if(argConst!=null && argConst.type !in possibleDts) {
-                        val convertedValue = argConst.cast(possibleDts.first())     // TODO can throw exception
+                        val convertedValue = argConst.cast(possibleDts.first())
                         functionCall.arglist[arg.first.index] = convertedValue
                         optimizationsDone++
                     }
@@ -226,7 +226,7 @@ class ConstantFolding(private val program: Program) : IAstModifyingVisitor {
                 val expectedDt = arg.second.type
                 val argConst = arg.first.value.constValue(program)
                 if(argConst!=null && argConst.type!=expectedDt) {
-                    val convertedValue = argConst.cast(expectedDt)  // TODO can throw exception
+                    val convertedValue = argConst.cast(expectedDt)
                     functionCall.arglist[arg.first.index] = convertedValue
                     optimizationsDone++
                 }
@@ -356,7 +356,7 @@ class ConstantFolding(private val program: Program) : IAstModifyingVisitor {
                                        subleftIsConst: Boolean,
                                        subrightIsConst: Boolean): Expression
     {
-        // @todo this implements only a small set of possible reorderings for now
+        // todo: this implements only a small set of possible reorderings at this time
         if(expr.operator==subExpr.operator) {
             // both operators are the isSameAs.
             // If + or *,  we can simply swap the const of expr and Var in subexpr.
@@ -544,11 +544,15 @@ class ConstantFolding(private val program: Program) : IAstModifyingVisitor {
     override fun visit(forLoop: ForLoop): Statement {
 
         fun adjustRangeDt(rangeFrom: NumericLiteralValue, targetDt: DataType, rangeTo: NumericLiteralValue, stepLiteral: NumericLiteralValue?, range: RangeExpr): RangeExpr {
-            // TODO casts can throw exception
-            val newFrom = rangeFrom.cast(targetDt)
-            val newTo = rangeTo.cast(targetDt)
-            val newStep: Expression =
-                    stepLiteral?.cast(targetDt) ?: range.step
+            val newFrom: NumericLiteralValue
+            val newTo: NumericLiteralValue
+            try {
+                newFrom = rangeFrom.cast(targetDt)
+                newTo = rangeTo.cast(targetDt)
+            } catch (x: ExpressionError) {
+                return range
+            }
+            val newStep: Expression = stepLiteral?.cast(targetDt) ?: range.step
             return RangeExpr(newFrom, newTo, newStep, range.position)
         }
 
diff --git a/compiler/test/UnitTests.kt b/compiler/test/UnitTests.kt
index 55f83b76a..b764f60a9 100644
--- a/compiler/test/UnitTests.kt
+++ b/compiler/test/UnitTests.kt
@@ -169,7 +169,15 @@ class TestZeropage {
         }
     }
 
-    // TODO test dontuse option
+    @Test
+    fun testZpDontuse() {
+        val zp = C64Zeropage(CompilationOptions(OutputType.RAW, LauncherType.NONE, ZeropageType.DONTUSE, emptyList(), false))
+        println(zp.free)
+        assertEquals(0, zp.available())
+        assertFailsWith<CompilerException> {
+            zp.allocate("", DataType.BYTE, null)
+        }
+    }
 
     @Test
     fun testFreeSpaces() {