diff --git a/src/main/scala/millfork/assembly/mos/opt/ReverseFlowAnalyzer.scala b/src/main/scala/millfork/assembly/mos/opt/ReverseFlowAnalyzer.scala
index 05d12a54..a6648036 100644
--- a/src/main/scala/millfork/assembly/mos/opt/ReverseFlowAnalyzer.scala
+++ b/src/main/scala/millfork/assembly/mos/opt/ReverseFlowAnalyzer.scala
@@ -169,6 +169,8 @@ object ReverseFlowAnalyzer {
                     result = result.copy(x = Important, y = Important)
                   case _ =>
                 })
+              case NormalParamSignature(List(MemoryVariable(_, typ, _))) if typ.size == 1 =>
+                result = result.copy(a = Important)
               case _ =>
             }
             if (ZeropageRegisterOptimizations.functionsThatUsePseudoregisterAsInput(fun.name)) {
diff --git a/src/main/scala/millfork/assembly/mos/opt/SingleAssignmentVariableOptimization.scala b/src/main/scala/millfork/assembly/mos/opt/SingleAssignmentVariableOptimization.scala
index 0fb6eec1..8b2f4fe3 100644
--- a/src/main/scala/millfork/assembly/mos/opt/SingleAssignmentVariableOptimization.scala
+++ b/src/main/scala/millfork/assembly/mos/opt/SingleAssignmentVariableOptimization.scala
@@ -35,6 +35,8 @@ object SingleAssignmentVariableOptimization extends AssemblyOptimization[Assembl
 
   override def optimize(f: NormalFunction, code: List[AssemblyLine], options: CompilationOptions): List[AssemblyLine] = {
     val paramVariables = f.params match {
+      case NormalParamSignature(List(MemoryVariable(_, typ, _))) if typ.size == 1 =>
+        Set[String]()
       case NormalParamSignature(ps) =>
         ps.map(_.name).toSet
       case _ =>
diff --git a/src/main/scala/millfork/assembly/mos/opt/VariableToRegisterOptimization.scala b/src/main/scala/millfork/assembly/mos/opt/VariableToRegisterOptimization.scala
index 64885d82..861ef03b 100644
--- a/src/main/scala/millfork/assembly/mos/opt/VariableToRegisterOptimization.scala
+++ b/src/main/scala/millfork/assembly/mos/opt/VariableToRegisterOptimization.scala
@@ -105,6 +105,8 @@ object VariableToRegisterOptimization extends AssemblyOptimization[AssemblyLine]
 
   override def optimize(f: NormalFunction, code: List[AssemblyLine], options: CompilationOptions): List[AssemblyLine] = {
     val paramVariables = f.params match {
+      case NormalParamSignature(List(MemoryVariable(_, typ, _))) if typ.size == 1 =>
+        Set[String]()
       case NormalParamSignature(ps) =>
         ps.map(_.name).toSet
       case _ =>
diff --git a/src/main/scala/millfork/compiler/mos/MosCompiler.scala b/src/main/scala/millfork/compiler/mos/MosCompiler.scala
index 5b4fdb73..f14a9350 100644
--- a/src/main/scala/millfork/compiler/mos/MosCompiler.scala
+++ b/src/main/scala/millfork/compiler/mos/MosCompiler.scala
@@ -23,6 +23,11 @@ object MosCompiler extends AbstractCompiler[AssemblyLine] {
     ctx.env.nameCheck(ctx.function.code)
     val chunk = MosStatementCompiler.compile(ctx, ctx.function.code)
 
+    val storeParamsFromRegisters = ctx.function.params match {
+      case NormalParamSignature(List(param@MemoryVariable(_, typ, _))) if typ.size == 1 =>
+        List(AssemblyLine.absolute(STA, param))
+      case _ => Nil
+    }
     val phReg =
       if (ctx.options.flag(CompilationFlag.ZeropagePseudoregister)) {
         val reg = ctx.env.get[VariableInMemory]("__reg")
@@ -34,7 +39,7 @@ object MosCompiler extends AbstractCompiler[AssemblyLine] {
         )
       } else Nil
 
-    val prefix = (if (ctx.function.interrupt) {
+    val prefix = storeParamsFromRegisters ++ (if (ctx.function.interrupt) {
 
       if (ctx.options.flag(CompilationFlag.EmitNative65816Opcodes)) {
         if (ctx.options.flag(CompilationFlag.ZeropagePseudoregister)) {
diff --git a/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala b/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
index ed7713c3..e76cd169 100644
--- a/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
+++ b/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
@@ -1067,6 +1067,8 @@ object MosExpressionCompiler extends AbstractExpressionCompiler[AssemblyLine] {
                       case _ => Nil
                     }
                     secondViaMemory ++ thirdViaRegisters :+ AssemblyLine.absoluteOrLongAbsolute(JSR, function, ctx.options)
+                  case NormalParamSignature(List(MemoryVariable(_, typ, _))) if typ.size == 1 =>
+                    compile(ctx, params.head, Some(b -> RegisterVariable(MosRegister.A, b)), BranchSpec.None) ++ List(AssemblyLine.absoluteOrLongAbsolute(JSR, function, ctx.options))
                   case NormalParamSignature(paramVars) =>
                     params.zip(paramVars).flatMap {
                       case (paramExpr, paramVar) =>