diff --git a/docs/api/command-line.md b/docs/api/command-line.md
index 63c6ef89..f87b6b51 100644
--- a/docs/api/command-line.md
+++ b/docs/api/command-line.md
@@ -212,12 +212,12 @@ Whether identical functions should be merged into one function.
 Default: yes. 
 
 * `-fsubroutine-extraction`, `-fno-subroutine-extraction` – 
-Whether identical fragments of functions should be extracted into subroutines.
+Whether identical fragments of functions should be extracted into subroutines (experimental).
+Makes the code smaller. Computationally very expensive.
 `.ini` equivalent: `subroutine_extraction`.
 Default: no. 
 
 * `-Os`, `--size` – Optimize for size, sacrificing some speed (experimental).
-Also enables `-fsubroutine-extraction`.
 
 * `-Of`, `--fast` – Optimize for speed, even if it increases the size a bit (experimental).
 Also enables `-finline`. 
diff --git a/src/main/scala/millfork/Context.scala b/src/main/scala/millfork/Context.scala
index d24d1147..a5247763 100644
--- a/src/main/scala/millfork/Context.scala
+++ b/src/main/scala/millfork/Context.scala
@@ -31,35 +31,34 @@ case class Context(errorReporting: Logger,
       copy(flags = this.flags + (f -> b))
     }
   }
+  
+  def isFlagSet(f: CompilationFlag.Value): Boolean = flags.getOrElse(f, false)
 
   def filloutFlags(): Context = {
     var addons = Map[CompilationFlag.Value, Boolean]()
-    if (flags.contains(CompilationFlag.EmitNative65816Opcodes)
-      || flags.contains(CompilationFlag.EmitEmulation65816Opcodes)
-      || flags.contains(CompilationFlag.EmitHudsonOpcodes)
-      || flags.contains(CompilationFlag.Emit65CE02Opcodes)) {
+    if (isFlagSet(CompilationFlag.EmitNative65816Opcodes)
+      || isFlagSet(CompilationFlag.EmitEmulation65816Opcodes)
+      || isFlagSet(CompilationFlag.EmitHudsonOpcodes)
+      || isFlagSet(CompilationFlag.Emit65CE02Opcodes)) {
       addons += CompilationFlag.EmitCmosOpcodes -> true
     }
-    if (flags.contains(CompilationFlag.EmitEZ80Opcodes)) {
+    if (isFlagSet(CompilationFlag.EmitEZ80Opcodes)) {
       addons += CompilationFlag.EmitZ80Opcodes -> true
     }
-    if (flags.contains(CompilationFlag.EmitZ80Opcodes) || flags.contains(CompilationFlag.EmitSharpOpcodes)) {
+    if (isFlagSet(CompilationFlag.EmitZ80Opcodes) || isFlagSet(CompilationFlag.EmitSharpOpcodes)) {
       addons += CompilationFlag.EmitExtended80Opcodes -> true
     }
-    if (flags.contains(CompilationFlag.EmitZ80Opcodes) || flags.contains(CompilationFlag.EmitIntel8085Opcodes)) {
+    if (isFlagSet(CompilationFlag.EmitZ80Opcodes) || isFlagSet(CompilationFlag.EmitIntel8085Opcodes)) {
       addons += CompilationFlag.EmitIntel8080Opcodes -> true
     }
-    if (flags.contains(CompilationFlag.OptimizeForSpeed)) {
+    if (isFlagSet(CompilationFlag.OptimizeForSpeed)) {
       addons += CompilationFlag.InlineFunctions -> true
     }
-    if (flags.contains(CompilationFlag.OptimizeForSize)) {
-      addons += CompilationFlag.SubroutineExtraction -> true
-    }
-    if (flags.contains(CompilationFlag.DangerousOptimizations)) {
+    if (isFlagSet(CompilationFlag.DangerousOptimizations)) {
       addons += CompilationFlag.InterproceduralOptimization -> true
       addons += CompilationFlag.OptimizeStdlib -> true
     }
-    if (flags.contains(CompilationFlag.OptimizeForDebugging)) {
+    if (isFlagSet(CompilationFlag.OptimizeForDebugging)) {
       addons += CompilationFlag.VariableOverlap -> false
       addons += CompilationFlag.RegisterVariables -> false
       addons += CompilationFlag.FunctionDeduplication -> false