diff --git a/HISTORY.markdown b/HISTORY.markdown
index fefecd8..4675caa 100644
--- a/HISTORY.markdown
+++ b/HISTORY.markdown
@@ -1,6 +1,11 @@
 History of SixtyPical
 =====================
 
+0.9
+---
+
+*   Add word (constant or memory location) to word memory location.
+
 0.8
 ---
 
diff --git a/README.markdown b/README.markdown
index 175c5e1..6092815 100644
--- a/README.markdown
+++ b/README.markdown
@@ -40,11 +40,11 @@ Documentation
 TODO
 ----
 
-### Add 16 bit values.
+### Operations on 16 bit values
 
-I guess this means making `add` a bit more like `copy`.
+Add word (constant or memory location) to pointer.  (Not necessarily range-checked yet though.)
 
-And then: add to pointer.  (Not necessarily range-checked yet though.)
+Compare word (constant or memory location) with memory location or pointer.  (Maybe?)
 
 And then write a little demo "game" where you can move a block around the screen with
 the joystick.
diff --git a/src/sixtypical/compiler.py b/src/sixtypical/compiler.py
index 3fd78e3..0f98d5a 100644
--- a/src/sixtypical/compiler.py
+++ b/src/sixtypical/compiler.py
@@ -147,14 +147,26 @@ class Compiler(object):
                     self.emitter.emit(ADC(Immediate(Byte(src.value))))
                 else:
                     self.emitter.emit(ADC(Absolute(self.labels[src.name])))
-            elif isinstance(src, ConstantRef) and isinstance(dest, LocationRef) and dest.type == TYPE_WORD:
-                dest_label = self.labels[dest.name]
-                self.emitter.emit(LDA(Absolute(dest_label)))
-                self.emitter.emit(ADC(Immediate(Byte(src.low_byte()))))
-                self.emitter.emit(STA(Absolute(dest_label)))
-                self.emitter.emit(LDA(Absolute(Offset(dest_label, 1))))
-                self.emitter.emit(ADC(Immediate(Byte(src.high_byte()))))
-                self.emitter.emit(STA(Absolute(Offset(dest_label, 1))))
+            elif isinstance(dest, LocationRef) and dest.type == TYPE_WORD and src.type == TYPE_WORD:
+                if isinstance(src, ConstantRef):
+                    dest_label = self.labels[dest.name]
+                    self.emitter.emit(LDA(Absolute(dest_label)))
+                    self.emitter.emit(ADC(Immediate(Byte(src.low_byte()))))
+                    self.emitter.emit(STA(Absolute(dest_label)))
+                    self.emitter.emit(LDA(Absolute(Offset(dest_label, 1))))
+                    self.emitter.emit(ADC(Immediate(Byte(src.high_byte()))))
+                    self.emitter.emit(STA(Absolute(Offset(dest_label, 1))))
+                elif isinstance(src, LocationRef):
+                    src_label = self.labels[src.name]
+                    dest_label = self.labels[dest.name]
+                    self.emitter.emit(LDA(Absolute(dest_label)))
+                    self.emitter.emit(ADC(Absolute(src_label)))
+                    self.emitter.emit(STA(Absolute(dest_label)))
+                    self.emitter.emit(LDA(Absolute(Offset(dest_label, 1))))
+                    self.emitter.emit(ADC(Absolute(Offset(src_label, 1))))
+                    self.emitter.emit(STA(Absolute(Offset(dest_label, 1))))
+                else:
+                    raise UnsupportedOpcodeError(instr)
             else:
                 raise UnsupportedOpcodeError(instr)
         elif opcode == 'sub':
diff --git a/tests/SixtyPical Analysis.md b/tests/SixtyPical Analysis.md
index c1afc13..e6813b5 100644
--- a/tests/SixtyPical Analysis.md	
+++ b/tests/SixtyPical Analysis.md	
@@ -412,6 +412,34 @@ To be sure, `add`ing a word constant to a word memory location trashes `a`.
     | }
     ? ForbiddenWriteError: a in main
 
+You can `add` a word memory location to another word memory location.
+
+    | word score
+    | word delta
+    | routine main
+    |   inputs score, delta
+    |   outputs score
+    |   trashes a, c, z, v, n
+    | {
+    |     st off, c
+    |     add score, delta
+    | }
+    = ok
+
+`add`ing a word memory location to a word memory location trashes `a`.
+
+    | word score
+    | word delta
+    | routine main
+    |   inputs score, delta
+    |   outputs score
+    |   trashes c, z, v, n
+    | {
+    |     st off, c
+    |     add score, delta
+    | }
+    ? ForbiddenWriteError: a in main
+
 ### sub ###
 
 Can't `sub` from or to a memory location that isn't initialized.
diff --git a/tests/SixtyPical Compilation.md b/tests/SixtyPical Compilation.md
index a9405b0..87d7378 100644
--- a/tests/SixtyPical Compilation.md	
+++ b/tests/SixtyPical Compilation.md	
@@ -344,11 +344,11 @@ goto.
 
 ### word operations
 
-Adding a constant word to a memory location.
+Adding a constant word to a word memory location.
 
     | word score
     | routine main
-    |   inputs a, score
+    |   inputs score
     |   outputs score
     |   trashes a, c, z, v, n
     | {
@@ -357,6 +357,20 @@ Adding a constant word to a memory location.
     | }
     = 00c018ad12c069cf8d12c0ad13c069078d13c060
 
+Adding a word memory location to another word memory location.
+
+    | word score
+    | word delta
+    | routine main
+    |   inputs score, delta
+    |   outputs score
+    |   trashes a, c, z, v, n
+    | {
+    |     st off, c
+    |     add score, delta
+    | }
+    = 00c018ad14c06d16c08d14c0ad15c06d17c08d15c060
+
 ### Buffers and Pointers
 
 Load address into pointer.