diff --git a/CHANGELOG.md b/CHANGELOG.md
index 560350be..6f16dbd7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,6 +32,8 @@
 
 * Minor improvements to inline assembly.
 
+* Improvements to constant evaluation.
+
 * Optimization improvements.
 
 ## 0.3.14
diff --git a/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala b/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
index 8bff6a64..ffe9620a 100644
--- a/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
+++ b/src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala
@@ -14,7 +14,8 @@ import millfork.output.NoAlignment
   */
 object MosExpressionCompiler extends AbstractExpressionCompiler[AssemblyLine] {
 
-  def compileConstant(ctx: CompilationContext, expr: Constant, exprType: Type, target: Variable): List[AssemblyLine] = {
+  def compileConstant(ctx: CompilationContext, expr0: Constant, exprType: Type, target: Variable): List[AssemblyLine] = {
+    val expr = expr0.fitInto(exprType, target.typ)
     target match {
       case RegisterVariable(MosRegister.A, _) => List(AssemblyLine(LDA, Immediate, expr))
       case RegisterVariable(MosRegister.AW, _) =>
diff --git a/src/main/scala/millfork/env/Constant.scala b/src/main/scala/millfork/env/Constant.scala
index 6fc09c30..11a832df 100644
--- a/src/main/scala/millfork/env/Constant.scala
+++ b/src/main/scala/millfork/env/Constant.scala
@@ -1,7 +1,7 @@
 package millfork.env
 
 import millfork.DecimalUtils._
-import millfork.node.ResolvedFieldDesc
+import millfork.node.{ResolvedFieldDesc, SumExpression}
 import millfork.output.DivisibleAlignment
 
 object Constant {
@@ -79,17 +79,19 @@ sealed trait Constant {
 
   def subword(index: Int): Constant = {
     if (requiredSize <= index) Constant.Zero
+    else if (requiredSize == 2 && !this.isInstanceOf[StructureConstant]) this
     else {
       // TODO: check if ok
-      CompoundConstant(MathOperator.Or, CompoundConstant(MathOperator.Shl, subbyte(index + 1), NumericConstant(8, 1)), subbyte(index)).quickSimplify
+      CompoundConstant(MathOperator.Or, CompoundConstant(MathOperator.Shl, subbyte(index + 1), NumericConstant(8, 2)), subbyte(index)).quickSimplify
     }
   }
 
   def subwordReversed(index: Int): Constant = {
     if (requiredSize <= index) Constant.Zero
+    else if (requiredSize == 2 && !this.isInstanceOf[StructureConstant]) this
     else {
       // TODO: check if ok
-      CompoundConstant(MathOperator.Or, CompoundConstant(MathOperator.Shl, subbyte(index), NumericConstant(8, 1)), subbyte(index + 1)).quickSimplify
+      CompoundConstant(MathOperator.Or, CompoundConstant(MathOperator.Shl, subbyte(index), NumericConstant(8, 2)), subbyte(index + 1)).quickSimplify
     }
   }
 
@@ -126,6 +128,10 @@ sealed trait Constant {
           case NumericConstant(value, 1) =>
             if (typ.isSigned) NumericConstant(value.toByte, 1)
             else NumericConstant(value & 0xff, 1)
+          case CompoundConstant(MathOperator.Minus, NumericConstant(l, _), NumericConstant(r, _)) =>
+            val value = l - r
+            if (typ.isSigned) NumericConstant(value.toByte, 1)
+            else NumericConstant(value & 0xff, 1)
           case b => b
         }
       case 2 =>
@@ -133,12 +139,26 @@ sealed trait Constant {
           case NumericConstant(value, _) =>
             if (typ.isSigned) NumericConstant(value.toShort, 2)
             else NumericConstant(value & 0xffff, 2)
+          case CompoundConstant(MathOperator.Minus, NumericConstant(l, _), NumericConstant(r, _)) =>
+            val value = l - r
+            if (typ.isSigned) NumericConstant(value.toShort, 2)
+            else NumericConstant(value & 0xffff, 2)
           case w => w
         }
       case _ => this
     }
   }
 
+  def fitInto(sourceType: Type, targetType: Type): Constant = {
+    val fit0 = fitInto(sourceType)
+    if (sourceType.size >= targetType.size) fit0 else {
+      fit0 match {
+        case NumericConstant(n, _) => NumericConstant(n, targetType.size)
+        case _ => fit0
+      }
+    }
+  }
+
   final def succ: Constant = (this + 1).quickSimplify
 
   def rootThingName: String
diff --git a/src/main/scala/millfork/output/AbstractAssembler.scala b/src/main/scala/millfork/output/AbstractAssembler.scala
index a13c36f8..2b09381d 100644
--- a/src/main/scala/millfork/output/AbstractAssembler.scala
+++ b/src/main/scala/millfork/output/AbstractAssembler.scala
@@ -140,11 +140,16 @@ abstract class AbstractAssembler[T <: AbstractCode](private val program: Program
         else ???
       case SubbyteConstant(cc, i) => deepConstResolve(cc).>>>(i * 8).&(0xff)
       case s: StructureConstant =>
-        s.typ.size match {
-          case 0 => 0
-          case 1 => deepConstResolve(s.subbyte(0))
-          case 2 => if (platform.isBigEndian) deepConstResolve(s.subwordReversed(0)) else deepConstResolve(s.subword(0)) // TODO: endianness?
-          case _ => ???
+        try {
+          s.typ.size match {
+            case 0 => 0
+            case 1 => deepConstResolve(s.subbyte(0))
+            case 2 => if (platform.isBigEndian) deepConstResolve(s.subwordReversed(0)) else deepConstResolve(s.subword(0)) // TODO: endianness?
+            case _ => ???
+          }
+        } catch {
+          case _: StackOverflowError =>
+            log.fatal("Stack overflow " + c)
         }
       case CompoundConstant(operator, lc, rc) =>
         val l = deepConstResolve(lc)
diff --git a/src/test/scala/millfork/test/StructSuite.scala b/src/test/scala/millfork/test/StructSuite.scala
index f9dce740..083834bb 100644
--- a/src/test/scala/millfork/test/StructSuite.scala
+++ b/src/test/scala/millfork/test/StructSuite.scala
@@ -92,7 +92,7 @@ class StructSuite extends FunSuite with Matchers {
   }
 
   test("Optimize struct modifications") {
-    EmuCrossPlatformBenchmarkRun(Cpu.Mos, Cpu.Z80, Cpu.Intel8086)("""
+    EmuCrossPlatformBenchmarkRun(Cpu.Mos, Cpu.Z80, Cpu.Intel8086, Cpu.Motorola6809)("""
         | struct point { byte x, byte y }
         | enum direction { none, right }
         | direction last_direction @$c400
@@ -116,7 +116,7 @@ class StructSuite extends FunSuite with Matchers {
   }
 
   test("Struct literals") {
-    EmuCrossPlatformBenchmarkRun(Cpu.Mos, Cpu.Z80, Cpu.Intel8086)("""
+    EmuCrossPlatformBenchmarkRun(Cpu.Mos, Cpu.Z80, Cpu.Intel8086, Cpu.Motorola6809)("""
         | struct point { byte x, byte y }
         | const point origin = point(1,2)
         | noinline point move_right(point p) {