diff --git a/src/main/scala/millfork/compiler/z80/ZBuiltIns.scala b/src/main/scala/millfork/compiler/z80/ZBuiltIns.scala
index 6bf1d47a..62ef995e 100644
--- a/src/main/scala/millfork/compiler/z80/ZBuiltIns.scala
+++ b/src/main/scala/millfork/compiler/z80/ZBuiltIns.scala
@@ -217,19 +217,24 @@ object ZBuiltIns {
           }
         case (true, expr) =>
           ctx.env.eval(expr) match {
-            case None =>
+            case Some(c) if hasConst && const.isProvablyGreaterOrEqualThan(c)=>
+              const = CompoundConstant(MathOperator.DecimalMinus, const, c).quickSimplify
+            case _ =>
               if (result.isEmpty) {
-                ???
-              } else if (ctx.options.flag(CompilationFlag.EmitExtended80Opcodes)) {
+                result += ZLine.ldImm16(ZRegister.HL, const)
+                const = NumericConstant(0, 2)
+                hasConst = false
+              }
+              if (ctx.options.flag(CompilationFlag.EmitExtended80Opcodes)) {
                 result += ZLine.ld8(ZRegister.E, ZRegister.L)
                 result += ZLine.ld8(ZRegister.D, ZRegister.H)
                 result ++= Z80ExpressionCompiler.stashDEIfChanged(ctx, Z80ExpressionCompiler.compileToHL(ctx, expr))
                 result += ZLine.ld8(ZRegister.A, ZRegister.E)
-                result += ZLine.registers(SUB, ZRegister.A, ZRegister.L)
+                result += ZLine.register(SUB, ZRegister.L)
                 result += ZLine.implied(DAA)
                 result += ZLine.ld8(ZRegister.L, ZRegister.A)
                 result += ZLine.ld8(ZRegister.A, ZRegister.D)
-                result += ZLine.registers(SBC, ZRegister.A, ZRegister.H)
+                result += ZLine.register(SBC, ZRegister.H)
                 result += ZLine.implied(DAA)
                 result += ZLine.ld8(ZRegister.H, ZRegister.A)
               } else {
@@ -248,9 +253,6 @@ object ZBuiltIns {
                 result += ZLine.implied(DAA)
                 result += ZLine.ld8(ZRegister.H, ZRegister.A)
               }
-            case Some(c) =>
-              hasConst = true
-              const = CompoundConstant(MathOperator.DecimalMinus, const, c).quickSimplify
           }
       }
     } else {
diff --git a/src/test/scala/millfork/test/WordMathSuite.scala b/src/test/scala/millfork/test/WordMathSuite.scala
index 7b08adf0..f436b45b 100644
--- a/src/test/scala/millfork/test/WordMathSuite.scala
+++ b/src/test/scala/millfork/test/WordMathSuite.scala
@@ -44,6 +44,21 @@ class WordMathSuite extends FunSuite with Matchers {
       """.stripMargin)(_.readWord(0xc000) should equal(240))
   }
 
+  test("Word subtraction 3") {
+    EmuCrossPlatformBenchmarkRun(Cpu.Cmos, Cpu.Z80, Cpu.Intel8080, Cpu.Sharp)("""
+        | word output @$c000
+        | word a
+        | void main () {
+        |  a = 640
+        |  f()
+        |  output = a - f()
+        | }
+        | word f() {
+        |   return 400
+        | }
+      """.stripMargin)(_.readWord(0xc000) should equal(240))
+  }
+
   test("Byte-to-word addition") {
     EmuCrossPlatformBenchmarkRun(Cpu.Mos, Cpu.Z80, Cpu.Intel8080, Cpu.Sharp)("""
         | word output @$c000