diff --git a/frontends/OccamPasses.hs b/frontends/OccamPasses.hs
index e669c9d..44f9050 100644
--- a/frontends/OccamPasses.hs
+++ b/frontends/OccamPasses.hs
@@ -79,13 +79,13 @@ foldConstants = applyDepthM2 doExpression doSpecification
         =  do (e', _, _) <- constantFold e
               return e'
 
-    -- When an expression is abbreviated, update its definition so that it can
-    -- be used when folding later expressions.
+    -- After we're done folding a specification, update its definition.
+    -- (Even if it isn't an expression itself, it might have others inside it,
+    -- so we just update them all.)
     doSpecification :: A.Specification -> PassM A.Specification
-    doSpecification s@(A.Specification _ n st@(A.IsExpr _ _ _ _))
+    doSpecification s@(A.Specification _ n st)
         =  do modifyName n (\nd -> nd { A.ndType = st })
               return s
-    doSpecification s = return s
 
 -- | Check that things that must be constant are.
 checkConstants :: Data t => t -> PassM t
diff --git a/testcases/const-array-dim.occ b/testcases/const-array-dim.occ
new file mode 100644
index 0000000..2d74e11
--- /dev/null
+++ b/testcases/const-array-dim.occ
@@ -0,0 +1,18 @@
+VAL INT screen.width IS 80:
+VAL INT screen.height IS 24:
+
+PROC clear.buffer ([screen.height][screen.width]BYTE screen, [screen.height][screen.width]INT colour)
+  SKIP
+:
+
+PROC screen.buffer (CHAN OF BYTE in, CHAN OF BYTE out)
+  [2][screen.height][screen.width]BYTE screen:
+  [2][screen.height][screen.width]INT colour:
+  SEQ
+    clear.buffer (screen[0], colour[0])
+    clear.buffer (screen[1], colour[1])
+:
+
+PROC q7 ()
+  SKIP
+: