diff --git a/Programs/CosmOS/README.md b/Programs/CosmOS/README.md
index 6e218bf..8c6bacc 100644
--- a/Programs/CosmOS/README.md
+++ b/Programs/CosmOS/README.md
@@ -263,6 +263,10 @@ prompt rather than at the shell.
 `x` and `d` share a position, and each leaves it after what it displayed, so either may be
 given without an address to continue from where the last one stopped.
 
+**Everything the shell does still works in the monitor**, since it is a mode of the shell
+rather than a different program: a program can be started by name, `dir` still lists, and a
+word that is nothing at all is still told so.
+
 For example:
 
 ```text
diff --git a/Programs/CosmOS/Source/cosmos.asm b/Programs/CosmOS/Source/cosmos.asm
index 354d966..5a89e55 100644
--- a/Programs/CosmOS/Source/cosmos.asm
+++ b/Programs/CosmOS/Source/cosmos.asm
@@ -331,6 +331,20 @@ promptWhere:
   CALL textSame
   BRQ doAssemble
 
+  ; ---- And a word the monitor does not know either ----
+  ;
+  ; It goes where the shell's unknown words go, which is the disk, because the monitor is a
+  ; MODE of the shell rather than a different program and everything the shell can do is
+  ; still supposed to work in it.
+  ;
+  ; THERE WAS NOTHING HERE AT ALL, and the fall through was into sayPrompt - a routine, which
+  ; ended in a RET that had nothing of its own to return to. So it took whatever the Stack
+  ; held and went there. Sometimes that was 0x0003, in the middle of newLine, and the machine
+  ; stopped on a byte that is not an instruction; once it was inside sbfsFormat, and the
+  ; machine formatted the disk it had booted from. The tell was a SECOND prompt printed
+  ; before the wreckage, which is sayPrompt doing exactly what it is for on its way past.
+  BRI promptUnknown
+
 ; Where you are, and then the prompt itself. A routine rather than a run of code in the loop,
 ; because the loop is no longer the only thing that needs it - see shellReadTyped.
 sayPrompt:
diff --git a/SplitBit Test Manual.md b/SplitBit Test Manual.md
index 88170ac..a66dbea 100644
--- a/SplitBit Test Manual.md	
+++ b/SplitBit Test Manual.md	
@@ -79,7 +79,7 @@ from `make`, not from here.
 ### 1. Recorded output
 
 `Tests/run.sh` assembles each program named in `Tests/manifest`, runs it, and compares
-everything it printed against a file in `Tests/expected`. 196 tests, of which 134 run, 35
+everything it printed against a file in `Tests/expected`. 197 tests, of which 135 run, 35
 only assemble, 16 are expected to fail to assemble, and 11 boot from ROM with no image
 given at all.
 
diff --git a/Tests/expected/cosmosMonitorRun.out b/Tests/expected/cosmosMonitorRun.out
new file mode 100644
index 0000000..5b58768
--- /dev/null
+++ b/Tests/expected/cosmosMonitorRun.out
@@ -0,0 +1,42 @@
+CosmOS
+> monitor
+x examine, d disassemble, a assemble, s set, b bank, g go, exit leaves
+* Say hello from the monitor
+it says: hello from the monitor
+finished
+* Crash opcode
+that byte is not an instruction, at 4081
+  A 00  B 0F  Q 00
+the program was stopped
+* nonsense
+I do not know: nonsense
+* b program
+bank 00
+* exit
+> dir
+greet.sbx               211
+hello.sbx               53
+Life.sbx                1396
+Snake.sbx               2164
+Keys.sbx                664
+Say.sbx                 156
+Break.sbx               149
+Grid.sbx                559
+Press.sbx               872
+Mode.sbx                48
+Crash.sbx               632
+notes.txt               21
+Apps                    <dir>
+hi.script               121
+bad.script              45
+plain.script            24
+cross.script            280
+nonl.script             38
+outer.script            376
+inner.script            44
+loop.script             35
+20 files, 1 directory
+> exit
+halted
+Execution halted.
+[exit 0]
diff --git a/Tests/input/cosmosMonitorRun.in b/Tests/input/cosmosMonitorRun.in
new file mode 100644
index 0000000..3a220da
--- /dev/null
+++ b/Tests/input/cosmosMonitorRun.in
@@ -0,0 +1,8 @@
+monitor
+Say hello from the monitor
+Crash opcode
+nonsense
+b program
+exit
+dir
+exit
diff --git a/Tests/manifest b/Tests/manifest
index 073b13b..f26d7a7 100644
--- a/Tests/manifest
+++ b/Tests/manifest
@@ -340,6 +340,16 @@ cosmosFault          | CosmOS/Source/cosmos.asm           | run      | cosmosFau
 # monitor by jumping into the unwritten space above CosmOS and below where programs load,
 # which is zeroes - so it faults at once and corrupts nothing on the way.
 cosmosFaultSystem    | CosmOS/Source/cosmos.asm           | run      | cosmosFaultSys.in  | -     | disks/cosmos.img
+# A word the MONITOR does not know. There was nothing at the end of its command list, so an
+# unrecognised word fell through into sayPrompt - a routine, whose RET then had nothing of its
+# own to return to and went wherever the Stack happened to point. That was 0x0003 in the
+# middle of newLine one time and inside sbfsFormat another, which formatted the disk the
+# machine had booted from.
+#
+# So all three cases are here: a program run by name, a program that faults, and a word that
+# is nothing at all. The monitor is a mode of the shell and everything the shell does is
+# meant to work in it.
+cosmosMonitorRun     | CosmOS/Source/cosmos.asm           | run      | cosmosMonitorRun.in | -    | disks/cosmos.img
 # The shell editing the line it is being given, which is the whole reason the keys were
 # made to arrive. Every line here is typed wrong and then corrected with a different key, and
 # every one of them comes out as the same command - so the recording says both what the