diff --git a/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala b/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala
index 002d6d2f..4f24ff4d 100644
--- a/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala
+++ b/src/main/scala/millfork/compiler/AbstractStatementPreprocessor.scala
@@ -231,8 +231,8 @@ abstract class AbstractStatementPreprocessor(protected val ctx: CompilationConte
               !env.overlapsVariable(f.variable, source) &&
               !env.overlapsVariable(f.variable, f.start) &&
               !env.overlapsVariable(f.variable, f.end) &&
-              source.isPure &&
-              sourceType.size == 1 &&
+              ctx.isConstant(source) &&
+              sourceType.size <= 1 &&
               targetType.size == 1 &&
               sourceType.isAssignableTo(targetType)
             ) {
@@ -738,9 +738,9 @@ object AbstractStatementPreprocessor {
         val sourceType = AbstractExpressionCompiler.getExpressionType(ctx, source)
         val targetType = AbstractExpressionCompiler.getExpressionType(ctx, target)
         if (
-          source.isPure &&
-          index.isPure &&
-          sourceType.size == 1 &&
+          ctx.isConstant(source) &&
+          ctx.isConstant(index) &&
+          sourceType.size <= 1 &&
           targetType.size == 1  &&
           sourceType.isAssignableTo(targetType)&&
           !env.isVolatile(VariableExpression(pointy)) &&
diff --git a/src/main/scala/millfork/compiler/CompilationContext.scala b/src/main/scala/millfork/compiler/CompilationContext.scala
index 53907630..244d71dc 100644
--- a/src/main/scala/millfork/compiler/CompilationContext.scala
+++ b/src/main/scala/millfork/compiler/CompilationContext.scala
@@ -2,7 +2,7 @@ package millfork.compiler
 
 import millfork.env.{Environment, Label, NormalFunction, NormalParamSignature}
 import millfork.error.Logger
-import millfork.node.NiceFunctionProperty
+import millfork.node.{Expression, NiceFunctionProperty}
 import millfork.{CompilationFlag, CompilationOptions, JobContext}
 
 /**
@@ -15,6 +15,9 @@ case class CompilationContext(env: Environment,
                               niceFunctionProperties: Set[(NiceFunctionProperty, String)],
                               breakLabels: Map[String, Label] = Map(),
                               continueLabels: Map[String, Label] = Map()){
+
+  def isConstant(v: Expression): Boolean = v.isPure || env.eval(v).isDefined
+
   def withInlinedEnv(environment: Environment, newLabel: String): CompilationContext = {
     val newEnv = new Environment(Some(env), newLabel, environment.cpuFamily, options)
     newEnv.things ++= environment.things
diff --git a/src/main/scala/millfork/compiler/mos/BuiltIns.scala b/src/main/scala/millfork/compiler/mos/BuiltIns.scala
index de396887..d5384072 100644
--- a/src/main/scala/millfork/compiler/mos/BuiltIns.scala
+++ b/src/main/scala/millfork/compiler/mos/BuiltIns.scala
@@ -1292,7 +1292,7 @@ object BuiltIns {
   def compileByteMultiplication(ctx: CompilationContext, v: Expression, c: Int): List[AssemblyLine] = {
     c match {
       case 0 =>
-        if (v.isPure) return List(AssemblyLine.immediate(LDA, 0))
+        if (ctx.isConstant(v)) return List(AssemblyLine.immediate(LDA, 0))
         else return MosExpressionCompiler.compileToA(ctx, v) ++ List(AssemblyLine.immediate(LDA, 0))
       case 1 => return MosExpressionCompiler.compileToA(ctx, v)
       case 2 | 4 | 8 | 16 | 32 =>
diff --git a/src/main/scala/millfork/compiler/z80/Z80BulkMemoryOperations.scala b/src/main/scala/millfork/compiler/z80/Z80BulkMemoryOperations.scala
index 4457be62..9bb641af 100644
--- a/src/main/scala/millfork/compiler/z80/Z80BulkMemoryOperations.scala
+++ b/src/main/scala/millfork/compiler/z80/Z80BulkMemoryOperations.scala
@@ -21,7 +21,7 @@ object Z80BulkMemoryOperations {
     */
   def compileMemcpy(ctx: CompilationContext, target: IndexedExpression, source: IndexedExpression, f: ForStatement): List[ZLine] = {
     val sourceOffset = removeVariableOnce(ctx, f.variable, source.index).getOrElse(return compileForStatement(ctx, f)._1)
-    if (!sourceOffset.isPure) return compileForStatement(ctx, f)._1
+    if (!ctx.isConstant(sourceOffset)) return compileForStatement(ctx, f)._1
     val sourceIndexExpression = sourceOffset #+# f.start
     val calculateSource = Z80ExpressionCompiler.calculateAddressToHL(ctx, IndexedExpression(source.name, sourceIndexExpression).pos(source.position), forWriting = false)
     compileMemoryBulk(ctx, target, f,
@@ -85,11 +85,11 @@ object Z80BulkMemoryOperations {
 
     if (ctx.options.flag(CompilationFlag.EmitZ80Opcodes)) {
       removeVariableOnce(ctx, f.variable, target.index) match {
-        case Some(targetOffset) if targetOffset.isPure =>
+        case Some(targetOffset) if ctx.isConstant(targetOffset) =>
           return compileForZ80(targetOffset)
         case _ =>
       }
-      if (target.isPure && target.name == f.variable && !ctx.env.overlapsVariable(f.variable, target.index)) {
+      if (ctx.isConstant(target) && target.name == f.variable && !ctx.env.overlapsVariable(f.variable, target.index)) {
         return compileForZ80(target.index)
       }
     }
@@ -437,7 +437,7 @@ object Z80BulkMemoryOperations {
     val pointy = ctx.env.getPointy(target.name)
     if (pointy.elementType.alignedSize > 1) return Z80StatementCompiler.compileForStatement(ctx, f)._1
     val targetOffset = removeVariableOnce(ctx, f.variable, target.index).getOrElse(return compileForStatement(ctx, f)._1)
-    if (!targetOffset.isPure) return compileForStatement(ctx, f)._1
+    if (!ctx.isConstant(targetOffset)) return compileForStatement(ctx, f)._1
     val indexVariableSize = ctx.env.get[Variable](f.variable).typ.size
     val wrapper = createForLoopPreconditioningIfStatement(ctx, f)
     val decreasingDespiteSyntax = preferDecreasing && (f.direction == ForDirection.ParallelTo || f.direction == ForDirection.ParallelUntil)