diff --git a/Programs/CosmOS/Assembler/source.asm b/Programs/CosmOS/Assembler/source.asm
index bc64c54..8993e7b 100644
--- a/Programs/CosmOS/Assembler/source.asm
+++ b/Programs/CosmOS/Assembler/source.asm
@@ -244,6 +244,26 @@ srcIncludeSkip:
   RET
 
 srcIncludeGone:
+  ; ---- Say which one ----
+  ;
+  ; It said nothing at all, and the assembler's catch-all then said "nothing was written" -
+  ; which is true and useless. Three programs on the disk could be read and not assembled,
+  ; and finding out why meant reading the assembler rather than the message.
+  ;
+  ; SrcName holds the library path by now, because that was the second place tried, so this
+  ; says where it looked as well as what for. Both are worth having: a name that is not in
+  ; /Lib and not beside you is usually one or the other spelt wrong.
+  SETD.0 GoneText
+  SWI osPrintString
+  SETD.0 IncWanted
+  SWI osPrintString
+  SETD.0 GoneWhereText
+  SWI osPrintString
+  SETD.0 SrcName
+  SWI osPrintString
+  SETD.0 GoneEndText
+  SWI osPrintString
+
   ; The file is not there. The stack is left as it is: the caller stops the assembly, and
   ; unwinding for the sake of tidiness would only hide where it happened.
   RSTA
@@ -596,6 +616,13 @@ IncSlot:
 IncSlotLeft:
   0x00
 
+GoneText:
+"cannot find "
+GoneWhereText:
+", not beside the file that asked and not as "
+GoneEndText:
+"
+"
 TooDeepText:
 "included files are nested deeper than this assembler will follow
 "
diff --git a/Programs/makefile b/Programs/makefile
index 200510a..06b8f14 100644
--- a/Programs/makefile
+++ b/Programs/makefile
@@ -129,6 +129,13 @@ cosmos: $(COSMOS) $(APPS) $(NATIVE_ASM)
 # blocks of four thousand and ninety six - three tenths of one per cent - to buy a hundred
 # and twenty eight more names. The superblock has carried this number per disk since the
 # format was written, so nothing but this line knows what it is.
+# ---- And on the recipe that lays it out ----
+#
+# Changing HOW the disk is built has to rebuild the disk. It did not, so adding the libraries
+# to /Lib left an image that had been made without them, and the next run said the same thing
+# was still missing - which sends you looking at the change you just made rather than at the
+# stale thing in front of you.
+$(COSMOS_DISK): makefile
 $(COSMOS_DISK): $(APPS) $(NATIVE_ASM) $(COSMOS) $(STAGE2) testPrograms/stringKeyword.asm \
                 $(wildcard CosmOS/Apps/*.asm) \
                 $(wildcard CosmOS/Source/*.asm) $(wildcard CosmOS/Assembler/*.asm)
@@ -190,6 +197,14 @@ $(COSMOS_DISK): $(APPS) $(NATIVE_ASM) $(COSMOS) $(STAGE2) testPrograms/stringKey
 	@# with a name longer than a directory entry holds is refused rather than skipped: a
 	@# disk quietly missing a file is the failure a mirror exists to prevent.
 	$(DISKTOOL) mirror $@ . /Source build
+	@# ---- And the libraries proper ----
+	@#
+	@# Programs/Libraries is what an #Include means when it is not a CosmOS source: print,
+	@# the integer helpers, the maths. They were never here, because /Lib was a hand-written
+	@# list and nobody thought of them - so Sieve-16.asm, Life.asm and Fib-16.asm could be
+	@# read on the machine and not assembled on it, and the assembler said only "nothing was
+	@# written". Mirrored, so that the next one nobody thinks of is here anyway.
+	$(DISKTOOL) mirror $@ Libraries /Lib
 	@for f in CosmOS/Source/console.asm CosmOS/Source/fileStream.asm \
 	          CosmOS/Source/sbfs.asm CosmOS/Source/services.asm CosmOS/Source/text.asm \
 	          CosmOS/Source/config.asm \