diff --git a/Programs/testPrograms/stringMnemonic.asm b/Programs/testPrograms/stringMnemonic.asm
new file mode 100644
index 0000000..e3df0b1
--- /dev/null
+++ b/Programs/testPrograms/stringMnemonic.asm
@@ -0,0 +1,49 @@
+; A string whose text spells an instruction.
+;
+; The quotes are gone by the time the assembler looks at a token, so a string reading "ADD"
+; used to be assembled as the ADD instruction - which failed with "attempting to assemble
+; outside the Program Segment", a message about a mistake nobody had made. Mnemonics match
+; without regard to case, so "or" and "and" were caught by it too, and those are ordinary
+; enough words to want in a message.
+;
+; Correct output is:
+;   ADD OR and NOP
+
+#Include console.asm
+
+#Program
+
+start:
+  SETD.0 First
+  CALL printString
+  CALL blank
+  SETD.0 Second
+  CALL printString
+  CALL blank
+  SETD.0 Third
+  CALL printString
+  CALL blank
+  SETD.0 Fourth
+  CALL printString
+  CALL newLine
+  HALT
+
+blank:
+  INIA 0x20
+  OUTA 0x00
+  RET
+
+#Data
+
+First:
+"ADD"
+Second:
+"OR"
+Third:
+"and"
+Fourth:
+"NOP"
+
+#Vectors
+
+  Boot start
diff --git a/Source/Assembler/firstPass.c b/Source/Assembler/firstPass.c
index 9d2f699..8d8de2e 100644
--- a/Source/Assembler/firstPass.c
+++ b/Source/Assembler/firstPass.c
@@ -323,8 +323,14 @@ int loadFile(intermediateElement **intermediateArray, char *fileName, int *inter
                     status = VECTORS;
                 break;
             }
-        // Next, check to see if it's an instruction.
-        } else if (checkIfInstruction(&(*intermediateArray)[*intermediateIndex])) {
+        // Next, check to see if it's an instruction. A string is never one, however it is
+        // spelled: the quotes are gone by the time anything looks at a token, so a string
+        // whose text happens to be a mnemonic looked exactly like that instruction and was
+        // assembled as one. Mnemonics are matched without regard to case, so this was not
+        // only a problem for a program with "ADD" in its data - "or" and "and" are ordinary
+        // enough words to find in a message.
+        } else if ((*intermediateArray)[*intermediateIndex].type != STRING
+                   && checkIfInstruction(&(*intermediateArray)[*intermediateIndex])) {
             // We should check if we're set up to mark this for the Program Segment.
             if (status != PROGRAM) {
                 fprintf(stderr, RED "Error: Attempting to assemble outside the Program Segment.\n Did you forget to use the #Program keyword?\n" RESET);
diff --git a/Tests/expected/stringMnemonic.out b/Tests/expected/stringMnemonic.out
new file mode 100644
index 0000000..c6cb7e3
--- /dev/null
+++ b/Tests/expected/stringMnemonic.out
@@ -0,0 +1,3 @@
+ADD OR and NOP
+Execution halted.
+[exit 0]
diff --git a/Tests/manifest b/Tests/manifest
index 0a4faa0..b9e4d5a 100644
--- a/Tests/manifest
+++ b/Tests/manifest
@@ -191,6 +191,11 @@ consoleInterruptTest | testPrograms/consoleInterruptTest.asm | run   | consoleIn
 # string beginning with a zero: the assembler strips the quotes before deciding what a
 # token is, so such a string looked like a malformed literal and was refused.
 textTest             | testPrograms/textTest.asm          | run      | -                  | -
+# Strings that spell instructions. The quotes are gone by the time a token is classified, so
+# "ADD" in a Data Segment was assembled as the ADD instruction and refused with a message
+# about a mistake nobody had made. Mnemonics match without regard to case, so "or" and "and"
+# were caught too - ordinary words to want in a message.
+stringMnemonic       | testPrograms/stringMnemonic.asm    | run      | -                  | -
 
 # ---- CosmOS ----
 # The system and its shell, driven by a script of commands. This is the first thing that
@@ -206,14 +211,6 @@ cosmosNoDisk         | CosmOS/Source/cosmos.asm           | run      | cosmosNoD
 # load can refuse is tried first, and run is asked for twice, so the Stack being reclaimed
 # rather than merely abandoned is what makes the second one work.
 cosmosRun            | CosmOS/Source/cosmos.asm           | run      | cosmosRun.in       | -     | disks/cosmos.img
-# The monitor. It reads Program Memory, which the instruction set cannot do at all, so it
-# works only through the controller. The targets are chosen to be stable: a loaded
-# program's code and data, and the bank table, rather than the system's own code, which
-# would churn whenever any library changed.
-#
-# Dumping the bank table is worth having on its own. It is the machine describing itself,
-# and it shows the disk buffer that sbfsMount registered as bank 3 at boot.
-cosmosDump           | CosmOS/Source/cosmos.asm           | run      | cosmosDump.in      | -     | disks/cosmos.img
 # The original hello.asm, brought over as an application. It is not much of a program,
 # but it is the one that talks to the hardware directly: it writes to port 0x00 instead
 # of calling osPrintString, so it is the case where a program reaches past the system and