diff --git a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt
index 38e228aa5..3782a710d 100644
--- a/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt
+++ b/codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt
@@ -1454,6 +1454,7 @@ internal class AssignmentAsmGen(private val program: PtProgram,
                     in ByteDatatypes -> {
                         assignExpressionToRegister(expr.left, RegisterOrPair.A, dt==DataType.BYTE)
                         asmgen.out("""
+                            cmp  #0
                             beq  +
                             lda  #1
 +                           eor  #1""")
diff --git a/compiler/res/prog8lib/cx16/diskio.p8 b/compiler/res/prog8lib/cx16/diskio.p8
index afa2639eb..090674789 100644
--- a/compiler/res/prog8lib/cx16/diskio.p8
+++ b/compiler/res/prog8lib/cx16/diskio.p8
@@ -32,8 +32,9 @@ diskio {
         cbm.CHKOUT(WRITE_IO_CHANNEL)
     }
 
-    sub fastmode(ubyte mode) {
-        ; -- set fast serial mode (0=none, 1=auto_tx, 2=fast writes, 3=both) for the SD card
+    sub fastmode(ubyte mode) -> bool {
+        ; -- set fast serial mode (0=none, 1=auto_tx, 2=fast writes, 3=both) for the SD card.
+        ;    Returns success status (fails on emulator host fs for example)
         list_filename[0] = 'u'
         list_filename[1] = '0'
         list_filename[2] = '>'
@@ -41,6 +42,7 @@ diskio {
         list_filename[4] = mode | $30
         list_filename[5] = 0
         send_command(list_filename)
+        return status_code()==0
     }
 
     sub directory() -> bool {
diff --git a/examples/test.p8 b/examples/test.p8
index 71bd6529c..bba164ac0 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -7,7 +7,18 @@
 
 main {
     sub start() {
-        txt.iso()
-        cx16.iso_cursor_char(iso:'_')
+        str command = "u0>b1"
+        diskio.send_command(command)
+        ;txt.print(diskio.status())
+        txt.print_bool(diskio.status_code()==0)
+        txt.nl()
+        txt.print_bool(status_code()==0)
+        txt.nl()
+        ;txt.print_bool(diskio.status_code()==0)
+    }
+
+    sub status_code() -> ubyte {
+        cx16.r0++
+        return 30
     }
 }