diff --git a/src/main/scala/millfork/compiler/mos/MosBulkMemoryOperations.scala b/src/main/scala/millfork/compiler/mos/MosBulkMemoryOperations.scala
index f1e0635a..ab79777e 100644
--- a/src/main/scala/millfork/compiler/mos/MosBulkMemoryOperations.scala
+++ b/src/main/scala/millfork/compiler/mos/MosBulkMemoryOperations.scala
@@ -3,7 +3,7 @@ package millfork.compiler.mos
 import millfork.CompilationFlag
 import millfork.assembly.mos.{AddrMode, AssemblyLine, AssemblyLine0, Opcode}
 import millfork.compiler.{AbstractExpressionCompiler, BranchSpec, CompilationContext}
-import millfork.env.{Label, MemoryAddressConstant, NumericConstant, Type, Variable, VariableInMemory}
+import millfork.env.{Label, MemoryAddressConstant, MemoryVariable, NumericConstant, RelativeVariable, Type, Variable, VariableAllocationMethod, VariableInMemory}
 import millfork.node._
 import millfork.assembly.mos.Opcode._
 
@@ -182,6 +182,13 @@ object MosBulkMemoryOperations {
     import ForDirection._
     val target = ctx.env.maybeGet[Variable](targetExpression.name).getOrElse(return None)
     if (target.isVolatile) return None
+    val indexVariable = ctx.env.get[Variable](f.variable)
+    if (indexVariable.isVolatile || indexVariable.typ.size != 1) return None
+    indexVariable match {
+      case v: MemoryVariable =>
+        if (v.alloc == VariableAllocationMethod.Static) return None
+      case _ => return None
+    }
     val sourceType = AbstractExpressionCompiler.getExpressionType(ctx, source)
     if (sourceType.size != 1) return None
     if (!sourceType.isArithmetic) return None
@@ -193,7 +200,6 @@ object MosBulkMemoryOperations {
       if (!target.typ.isArithmetic) return None
       if (target.typ.size != 1) return None
     }
-    val indexVariable = ctx.env.get[Variable](f.variable)
     val loadSource = MosExpressionCompiler.compileToA(ctx, source) match {
       case List(AssemblyLine0(LDY, Absolute | ZeroPage, MemoryAddressConstant(index)), l@AssemblyLine0(LDA, AbsoluteY | IndexedY, _)) if index.name == indexVariable.name => l
       case List(l@AssemblyLine0(LDA, Absolute | ZeroPage | Immediate, _)) => l
diff --git a/src/main/scala/millfork/compiler/mos/MosStatementCompiler.scala b/src/main/scala/millfork/compiler/mos/MosStatementCompiler.scala
index 38d4fe4c..464f4095 100644
--- a/src/main/scala/millfork/compiler/mos/MosStatementCompiler.scala
+++ b/src/main/scala/millfork/compiler/mos/MosStatementCompiler.scala
@@ -285,8 +285,9 @@ object MosStatementCompiler extends AbstractStatementCompiler[AssemblyLine] {
         compileDoWhileStatement(ctx, s)
       case f@ForStatement(variable, _, _, _, List(Assignment(target: IndexedExpression, source: Expression))) if !source.containsVariable(variable) =>
         MosBulkMemoryOperations.compileMemset(ctx, target, source, f) -> Nil
-      case f@ForStatement(variable, start, end, _, List(ExpressionStatement(FunctionCallExpression(operator@("+=" | "-=" | "+'=" | "-'=" | "|=" | "^=" | "&="), List(target: VariableExpression, source)))))
-        if !target.containsVariable(variable) && !start.containsVariable(target.name) && !end.containsVariable(target.name) =>
+      case f@ForStatement(variable, start, end, _, List(ExpressionStatement(
+        FunctionCallExpression(operator@("+=" | "-=" | "+'=" | "-'=" | "|=" | "^=" | "&="), List(target: VariableExpression, source))
+      ))) if !target.containsVariable(variable) && !source.containsVariable(variable) && !start.containsVariable(target.name) && !end.containsVariable(target.name) =>
         MosBulkMemoryOperations.compileFold(ctx, target, operator, source, f) match {
           case Some(x) => x -> Nil
           case None => compileForStatement(ctx, f)