diff --git a/compiler/src/prog8/compiler/astprocessing/AstChecker.kt b/compiler/src/prog8/compiler/astprocessing/AstChecker.kt
index 03e15f52f..fbe0687c7 100644
--- a/compiler/src/prog8/compiler/astprocessing/AstChecker.kt
+++ b/compiler/src/prog8/compiler/astprocessing/AstChecker.kt
@@ -451,66 +451,49 @@ internal class AstChecker(private val program: Program,
                 }
             }
 
-            val regCounts = mutableMapOf<CpuRegister, Int>().withDefault { 0 }
-            val statusflagCounts = mutableMapOf<Statusflag, Int>().withDefault { 0 }
+            val regsUsed = mutableListOf<RegisterOrPair>()
+            val statusflagUsed = mutableListOf<Statusflag>()
             fun countRegisters(from: Iterable<RegisterOrStatusflag>) {
-                regCounts.clear()
-                statusflagCounts.clear()
+                regsUsed.clear()
+                statusflagUsed.clear()
                 for(p in from) {
                     when(p.registerOrPair) {
-                        RegisterOrPair.A -> regCounts[CpuRegister.A]=regCounts.getValue(CpuRegister.A)+1
-                        RegisterOrPair.X -> regCounts[CpuRegister.X]=regCounts.getValue(CpuRegister.X)+1
-                        RegisterOrPair.Y -> regCounts[CpuRegister.Y]=regCounts.getValue(CpuRegister.Y)+1
+                        null -> {
+                            if (p.statusflag != null)
+                                statusflagUsed += p.statusflag!!
+                        }
                         RegisterOrPair.AX -> {
-                            regCounts[CpuRegister.A]=regCounts.getValue(CpuRegister.A)+1
-                            regCounts[CpuRegister.X]=regCounts.getValue(CpuRegister.X)+1
+                            regsUsed += RegisterOrPair.A
+                            regsUsed += RegisterOrPair.X
                         }
                         RegisterOrPair.AY -> {
-                            regCounts[CpuRegister.A]=regCounts.getValue(CpuRegister.A)+1
-                            regCounts[CpuRegister.Y]=regCounts.getValue(CpuRegister.Y)+1
+                            regsUsed += RegisterOrPair.A
+                            regsUsed += RegisterOrPair.Y
                         }
                         RegisterOrPair.XY -> {
-                            regCounts[CpuRegister.X]=regCounts.getValue(CpuRegister.X)+1
-                            regCounts[CpuRegister.Y]=regCounts.getValue(CpuRegister.Y)+1
-                        }
-                        RegisterOrPair.FAC1, RegisterOrPair.FAC2 -> { /* no sensible way to count this */ }
-                        RegisterOrPair.R0,
-                        RegisterOrPair.R1,
-                        RegisterOrPair.R2,
-                        RegisterOrPair.R3,
-                        RegisterOrPair.R4,
-                        RegisterOrPair.R5,
-                        RegisterOrPair.R6,
-                        RegisterOrPair.R7,
-                        RegisterOrPair.R8,
-                        RegisterOrPair.R9,
-                        RegisterOrPair.R10,
-                        RegisterOrPair.R11,
-                        RegisterOrPair.R12,
-                        RegisterOrPair.R13,
-                        RegisterOrPair.R14,
-                        RegisterOrPair.R15 -> { /* no sensible way to count this */ }
-                        null -> {
-                            val statusf = p.statusflag
-                            if (statusf != null)
-                                statusflagCounts[statusf] = statusflagCounts.getValue(statusf) + 1
+                            regsUsed += RegisterOrPair.X
+                            regsUsed += RegisterOrPair.Y
                         }
+                        else -> regsUsed += p.registerOrPair!!
                     }
                 }
             }
             countRegisters(subroutine.asmParameterRegisters)
-            if(regCounts.any{it.value>1})
+            if(regsUsed.size != regsUsed.toSet().size)
                 err("a register is used multiple times in the parameters")
-            if(statusflagCounts.any{it.value>1})
+            if(statusflagUsed.size != statusflagUsed.toSet().size)
                 err("a status flag is used multiple times in the parameters")
+
             countRegisters(subroutine.asmReturnvaluesRegisters)
-            if(regCounts.any{it.value>1})
+            if(regsUsed.size != regsUsed.toSet().size)
                 err("a register is used multiple times in the return values")
-            if(statusflagCounts.any{it.value>1})
+            if(statusflagUsed.size != statusflagUsed.toSet().size)
                 err("a status flag is used multiple times in the return values")
 
-            if(subroutine.asmClobbers.intersect(regCounts.keys).isNotEmpty())
-                err("a return register is also in the clobber list")
+            for(reg in subroutine.asmClobbers) {
+                if(regsUsed.contains(RegisterOrPair.fromCpuRegister(reg)))
+                    err("a return register is also in the clobber list")
+            }
 
             if(subroutine.statements.any{it !is InlineAssembly})
                 err("asmsub can only contain inline assembly (%asm)")
diff --git a/examples/test.p8 b/examples/test.p8
index c8038ce8e..8def12622 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -3,31 +3,34 @@
 
 main {
     sub start() {
-        const long foo2  = $123456
-        cx16.r0 = $ffff
-        cx16.r1 = $ea31
-        txt.print_uwbin(cx16.r1 << 7, true)
-        txt.nl()
-        txt.print_uwhex(cx16.r0 ^ cx16.r1, true)
-        txt.nl()
-        txt.print_ubhex(^cx16.r0, true)
-        txt.spc()
-        txt.print_uwhex(<<cx16.r0, false)
-        txt.nl()
-        txt.print_ubhex(^foo2, true)
-        txt.spc()
-        txt.print_uwhex(<<foo2, false)
-        txt.nl()
-        txt.print_ubhex(bankof(foo2), true)
-        txt.spc()
-        txt.print_uwhex(foo2 &$ffff, false)
+        foo(42)
+        bar(9999,55)
         txt.nl()
+        test(1,2,3)
+        test2(1)
+    }
 
-        txt.print_ubhex(msw(foo2), true)
-        txt.spc()
-        txt.print_uwhex(lsw(foo2), false)
+    sub foo(ubyte arg) {
+        txt.print_ub(arg)
         txt.nl()
+    }
 
+    sub bar(uword arg, ubyte arg2) {
+        txt.print_uw(arg)
+        txt.spc()
+        txt.print_ub(arg2)
+        txt.nl()
+    }
 
+    asmsub test(ubyte a1 @R1, ubyte a2 @R1, ubyte a3 @R2) {      ; TODO should give register reuse error
+        %asm {{
+            rts
+        }}
+    }
+
+    asmsub test2(uword a1 @AY) clobbers(A, X) -> ubyte @X {
+        %asm {{
+            rts
+        }}
     }
 }