diff --git a/doc/SixtyPical.md b/doc/SixtyPical.md
index 5e6fd8b..7eaddc5 100644
--- a/doc/SixtyPical.md
+++ b/doc/SixtyPical.md
@@ -334,8 +334,8 @@ To simulate a "while" loop, use an `if` internal to the block, like
     copy <src-memory-location>, <dest-memory-location>
 
 Reads from src and writes to dest.  Differs from `st` in that is able to
-copy more general types of data (for example, vectors,) and it sets the
-`z` and `n` flags and trashes the `a` register.
+copy more general types of data (for example, vectors,) and it trashes the
+`z` and `n` flags and the `a` register.
 
 *   It is illegal if dest is read-only.
 *   It is illegal if dest does not occur in the WRITES lists of the current
@@ -343,8 +343,8 @@ copy more general types of data (for example, vectors,) and it sets the
 *   It is illegal if src is not of same type as dest.
 *   It is illegal if src is uninitialized.
 
-After execution, dest is considered initialized, as are `z` and `n`, while
-`a` is considered uninitialized.
+After execution, dest is considered initialized, and `z` and `n`, and
+`a` are considered uninitialized.
 
 Grammar
 -------
diff --git a/src/sixtypical/analyzer.py b/src/sixtypical/analyzer.py
index 9ab4053..d615ca5 100644
--- a/src/sixtypical/analyzer.py
+++ b/src/sixtypical/analyzer.py
@@ -2,8 +2,9 @@
 
 from sixtypical.ast import Program, Routine, Block, Instr
 from sixtypical.model import (
-    TYPE_BYTE, TYPE_BYTE_TABLE,
-    ConstantRef, LocationRef, FLAG_Z, FLAG_N, FLAG_V, FLAG_C
+    TYPE_BYTE, TYPE_BYTE_TABLE, TYPE_ROUTINE, TYPE_VECTOR,
+    ConstantRef, LocationRef,
+    REG_A, FLAG_Z, FLAG_N, FLAG_V, FLAG_C
 )
 
 
@@ -214,5 +215,16 @@ def analyze_instr(instr, context, routines):
         analyze_block(instr.block, context, routines)
 
         # NB I *think* that's enough... but it might not be?
+    elif opcode == 'copy':
+        if src.type == dest.type:
+            pass
+        elif src.type == TYPE_ROUTINE and dest.type == TYPE_VECTOR:
+            pass
+        else:
+            raise TypeMismatchError((src, dest))
+        context.assert_initialized(src)
+        context.assert_writeable(dest)
+        context.set_initialized(dest)
+        context.set_uninitialized(REG_A, FLAG_Z, FLAG_N)
     else:
         raise NotImplementedError(opcode)
diff --git a/src/sixtypical/evaluator.py b/src/sixtypical/evaluator.py
index 2c9fbb4..e69bbaf 100644
--- a/src/sixtypical/evaluator.py
+++ b/src/sixtypical/evaluator.py
@@ -154,5 +154,11 @@ def eval_instr(instr, context, routines):
         eval_block(instr.block, context, routines)
         while context.get(src) == 0:
             eval_block(instr.block, context, routines)
+    elif opcode == 'copy':
+        context.set(dest, context.get(src))
+        # these are trashed; so could be anything really
+        context.set(REG_A, 0)
+        context.set(FLAG_Z, 0)
+        context.set(FLAG_N, 0)
     else:
         raise NotImplementedError
diff --git a/tests/SixtyPical Analysis.md b/tests/SixtyPical Analysis.md
index fcc84fb..e0b9db0 100644
--- a/tests/SixtyPical Analysis.md	
+++ b/tests/SixtyPical Analysis.md	
@@ -965,3 +965,74 @@ initialized at the start.
     |     } until z
     | }
     ? UninitializedAccessError: y
+
+### copy ###
+
+Can't `copy` from a memory location that isn't initialized.
+
+    | byte lives
+    | routine main
+    |   inputs x
+    |   outputs lives
+    |   trashes a, z, n
+    | {
+    |     copy x, lives
+    | }
+    = ok
+
+    | byte lives
+    | routine main
+    |   outputs lives
+    |   trashes x, a, z, n
+    | {
+    |     copy x, lives
+    | }
+    ? UninitializedAccessError: x
+
+Can't `st` to a memory location that doesn't appear in (outputs ∪ trashes).
+
+    | byte lives
+    | routine main
+    |   trashes lives, a, z, n
+    | {
+    |     copy 0, lives
+    | }
+    = ok
+
+    | byte lives
+    | routine main
+    |   outputs lives
+    |   trashes a, z, n
+    | {
+    |     copy 0, lives
+    | }
+    = ok
+
+    | byte lives
+    | routine main
+    |   inputs lives
+    |   trashes a, z, n
+    | {
+    |     copy 0, lives
+    | }
+    ? IllegalWriteError: lives
+
+a, z, and n are trashed, and must be declared as such
+
+    | byte lives
+    | routine main
+    |   outputs lives
+    | {
+    |     copy 0, lives
+    | }
+    ? IllegalWriteError: a
+
+a, z, and n are trashed, and must not be declared as outputs.
+
+    | byte lives
+    | routine main
+    |   outputs lives, a, z, n
+    | {
+    |     copy 0, lives
+    | }
+    ? UninitializedOutputError: a
diff --git a/tests/SixtyPical Execution.md b/tests/SixtyPical Execution.md
index 421776e..9570d63 100644
--- a/tests/SixtyPical Execution.md	
+++ b/tests/SixtyPical Execution.md	
@@ -385,3 +385,18 @@ Repeat loop.
     = x: 10
     = y: 25
     = z: 1
+
+Copy instruction.  Note that the state of a, z, and n are not defined
+after copy executes.
+
+    | routine main {
+    |     ld x, 5
+    |     copy x, y
+    | }
+    = a: 0
+    = c: 0
+    = n: 0
+    = v: 0
+    = x: 5
+    = y: 5
+    = z: 0