diff --git a/compiler/src/prog8/compiler/target/c64/codegen/BuiltinFunctionsAsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/BuiltinFunctionsAsmGen.kt
index 4f05dae82..638a79e0e 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/BuiltinFunctionsAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/BuiltinFunctionsAsmGen.kt
@@ -540,14 +540,21 @@ internal class BuiltinFunctionsAsmGen(private val program: Program, private val
     }
 
     private fun funcStrlen(fcall: IFunctionCall, resultToStack: Boolean) {
-        val name = asmgen.asmVariableName(fcall.args[0] as IdentifierReference)
-        val type = fcall.args[0].inferType(program)
-        when {
-            type.istype(DataType.STR) -> asmgen.out("  lda  #<$name |  ldy  #>$name")
-            type.istype(DataType.UWORD) -> asmgen.out("  lda  $name |  ldy  $name+1")
-            else -> throw AssemblyError("strlen requires str or uword arg")
+        if (fcall.args[0] is IdentifierReference) {
+            // use the address of the variable
+            val name = asmgen.asmVariableName(fcall.args[0] as IdentifierReference)
+            val type = fcall.args[0].inferType(program)
+            when {
+                type.istype(DataType.STR) -> asmgen.out("  lda  #<$name |  ldy  #>$name")
+                type.istype(DataType.UWORD) -> asmgen.out("  lda  $name |  ldy  $name+1")
+                else -> throw AssemblyError("strlen requires str or uword arg")
+            }
         }
-        if(resultToStack)
+        else {
+            // use the expression value as address of the string
+            asmgen.assignExpressionToRegister(fcall.args[0], RegisterOrPair.AY)
+        }
+        if (resultToStack)
             asmgen.out("  jsr  prog8_lib.func_strlen_stack")
         else
             asmgen.out("  jsr  prog8_lib.func_strlen_into_A")
diff --git a/compiler/src/prog8/functions/BuiltinFunctions.kt b/compiler/src/prog8/functions/BuiltinFunctions.kt
index 2a48755a6..43b2580ae 100644
--- a/compiler/src/prog8/functions/BuiltinFunctions.kt
+++ b/compiler/src/prog8/functions/BuiltinFunctions.kt
@@ -354,7 +354,7 @@ private fun builtinStrlen(args: List<Expression>, position: Position, program: P
     val argument=args[0]
     if(argument is StringLiteralValue)
         return NumericLiteralValue.optimalInteger(argument.value.length, argument.position)
-    val vardecl = (argument as IdentifierReference).targetVarDecl(program.namespace)
+    val vardecl = (argument as? IdentifierReference)?.targetVarDecl(program.namespace)
     if(vardecl!=null) {
         if(vardecl.datatype!=DataType.STR && vardecl.datatype!=DataType.UWORD)
             throw SyntaxError("strlen must have string argument", position)