diff --git a/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt
index db7d0752b..5ff1340fd 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/FunctionCallAsmGen.kt
@@ -177,13 +177,22 @@ internal class FunctionCallAsmGen(private val program: Program, private val asmg
         val statusflag = paramRegister.statusflag
         val register = paramRegister.registerOrPair
         val stack = paramRegister.stack
+        val requiredDt = parameter.value.type
+        if(requiredDt!=valueDt) {
+            if(valueDt.largerThan(requiredDt))
+                throw AssemblyError("can only convert byte values to word param types")
+        }
         when {
             stack -> {
                 // push arg onto the stack
                 // note: argument order is reversed (first argument will be deepest on the stack)
                 asmgen.translateExpression(value)
+                if(requiredDt!=valueDt)
+                    asmgen.signExtendStackLsb(valueDt)
             }
             statusflag!=null -> {
+                if(requiredDt!=valueDt)
+                    throw AssemblyError("for statusflag, byte value is required")
                 if (statusflag == Statusflag.Pc) {
                     // this param needs to be set last, right before the jsr
                     // for now, this is already enforced on the subroutine definition by the Ast Checker
@@ -235,6 +244,7 @@ internal class FunctionCallAsmGen(private val program: Program, private val asmg
                     AsmAssignSource.fromAstSource(value, program).adjustDataTypeToTarget(target)
                 }
 
+                // the following routine knows about converting byte to word if required:
                 asmgen.translateNormalAssignment(AsmAssignment(src, target, false, Position.DUMMY))
             }
         }
diff --git a/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt
index c918861e0..46cfe9e4f 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/assignment/AssignmentAsmGen.kt
@@ -34,7 +34,7 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
             SourceStorageKind.LITERALNUMBER -> {
                 // simple case: assign a constant number
                 val num = assign.source.number!!.number
-                when (assign.source.datatype) {
+                when (assign.target.datatype) {
                     DataType.UBYTE, DataType.BYTE -> assignConstantByte(assign.target, num.toShort())
                     DataType.UWORD, DataType.WORD -> assignConstantWord(assign.target, num.toInt())
                     DataType.FLOAT -> assignConstantFloat(assign.target, num.toDouble())
@@ -44,7 +44,7 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
             SourceStorageKind.VARIABLE -> {
                 // simple case: assign from another variable
                 val variable = assign.source.variable!!
-                when (assign.source.datatype) {
+                when (assign.target.datatype) {
                     DataType.UBYTE, DataType.BYTE -> assignVariableByte(assign.target, variable)
                     DataType.UWORD, DataType.WORD -> assignVariableWord(assign.target, variable)
                     DataType.FLOAT -> assignVariableFloat(assign.target, variable)
@@ -143,12 +143,16 @@ internal class AssignmentAsmGen(private val program: Program, private val asmgen
                         } else {
                             // regular subroutine, return values are (for now) always done via the stack...  TODO optimize this
                             asmgen.translateExpression(value)
+                            if(assign.target.datatype in WordDatatypes && assign.source.datatype in ByteDatatypes)
+                                asmgen.signExtendStackLsb(assign.source.datatype)
                             assignStackValue(assign.target)
                         }
                     }
                     else -> {
                         // everything else just evaluate via the stack.
                         asmgen.translateExpression(value)
+                        if(assign.target.datatype in WordDatatypes && assign.source.datatype in ByteDatatypes)
+                            asmgen.signExtendStackLsb(assign.source.datatype)
                         assignStackValue(assign.target)
                     }
                 }
diff --git a/examples/test.p8 b/examples/test.p8
index d6537eff7..245a4baec 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -13,28 +13,26 @@ main {
 ;            "sell  teleport  market  hold\n" +
 ;            "fuel  galhyp    local   quit\n")
 
-        str name = "irmen de jong"
-        uword strptr = &name
-
-
-        txt.print_ub(strlen("1234"))
-        txt.chrout('\n')
-        txt.print_ub(strlen(name))
-        txt.chrout('\n')
-        txt.print_uwhex(strptr, 1)
-        txt.chrout('\n')
-        txt.print(strptr)
-        txt.chrout('\n')
-        txt.print_ub(strlen(strptr))
-        txt.chrout('\n')
+;        str name = "irmen de jong"
+;        uword strptr = &name
+;
+;
+;        txt.print_ub(strlen("1234"))
+;        txt.chrout('\n')
+;        txt.print_ub(strlen(name))
+;        txt.chrout('\n')
+;        txt.print_uwhex(strptr, 1)
+;        txt.chrout('\n')
+;        txt.print(strptr)
+;        txt.chrout('\n')
+;        txt.print_ub(strlen(strptr))
+;        txt.chrout('\n')
 
         ubyte q
         for q in 0 to 255 {
             txt.print_ub(q)
             txt.chrout(' ')
-            ;txt.print_uw(q*4)       ; TODO fix
-;            txt.chrout(' ')
-            txt.print_uw(q*$0004)       ; TODO fix
+            txt.print_uw(q*5)       ; TODO fix
             txt.chrout('\n')
         }