diff --git a/lips/Collector.lua b/lips/Collector.lua
index a4ce389..34da262 100644
--- a/lips/Collector.lua
+++ b/lips/Collector.lua
@@ -160,8 +160,9 @@ function Collector:instruction()
         elseif self.tt == 'UNARY' then
             local peek = self.tokens[self.i + 1]
             if peek.tt == 'VARSYM' then
+                local negate = t.tok == -1
                 t = self:advance()
-                t = Token(t):set('negate')
+                t = Token(t):set('negate', negate)
                 insert(s, t)
                 self:advance()
             elseif peek.tt == 'EOL' or peek.tt == 'SEP' then
diff --git a/lips/Dumper.lua b/lips/Dumper.lua
index dde559b..8163365 100644
--- a/lips/Dumper.lua
+++ b/lips/Dumper.lua
@@ -73,47 +73,6 @@ function Dumper:desym(t)
     error('Internal Error: failed to desym')
 end
 
-function Dumper:toval(t)
-    if type(t) == 'number' then
-        return t
-    end
-
-    assert(type(t) == 'table', 'Internal Error: invalid value')
-
-    local val = self:desym(t)
-
-    if t.index then
-        val = val % 0x80000000
-        val = floor(val/4)
-    end
-    if t.negate then
-        val = -val
-    end
-
-    if t.portion == 'upper' then
-        val = bitrange(val, 16, 31)
-    elseif t.portion == 'lower' then
-        val = bitrange(val, 0, 15)
-    elseif t.portion == 'upperoff' then
-        local upper = bitrange(val, 16, 31)
-        local lower = bitrange(val, 0, 15)
-        if lower >= 0x8000 then
-            -- accommodate for offsets being signed
-            upper = (upper + 1) % 0x10000
-        end
-        val = upper
-    end
-
-    if t.negate or t.signed then
-        if val >= 0x10000 or val < -0x8000 then
-            self:error('value out of range', val)
-        end
-        val = val % 0x10000
-    end
-
-    return val
-end
-
 function Dumper:validate(n, bits)
     local max = 2^bits
     if n == nil then
@@ -126,7 +85,16 @@ function Dumper:validate(n, bits)
 end
 
 function Dumper:valvar(t, bits)
-    local val = self:toval(t)
+    local val = t
+    local err
+    if type(val) ~= 'number' then
+        t.tok = self:desym(t)
+        t.tt = 'NUM'
+        val, err = t:compute()
+        if err then
+            self:error(err, val)
+        end
+    end
     return self:validate(val, bits)
 end
 
diff --git a/lips/Token.lua b/lips/Token.lua
index a3ccc4a..4b94a56 100644
--- a/lips/Token.lua
+++ b/lips/Token.lua
@@ -1,5 +1,10 @@
+local floor = math.floor
+
 local path = string.gsub(..., "[^.]+$", "")
 local Base = require(path.."Base")
+local util = require(path.."util")
+
+local bitrange = util.bitrange
 
 local Token = Base:extend()
 function Token:init(...)
@@ -63,4 +68,39 @@ function Token:set(key, value)
     return self
 end
 
+function Token:compute()
+    assert(self.tt == 'NUM', 'Internal Error: cannot compute a non-number token')
+    local n = self.tok
+    if self.index then
+        n = n % 0x80000000
+        n = floor(n/4)
+    end
+    if self.negate then
+        n = -n
+    end
+
+    if self.portion == 'upper' then
+        n = bitrange(n, 16, 31)
+    elseif self.portion == 'lower' then
+        n = bitrange(n, 0, 15)
+    elseif self.portion == 'upperoff' then
+        local upper = bitrange(n, 16, 31)
+        local lower = bitrange(n, 0, 15)
+        if lower >= 0x8000 then
+            -- accommodate for offsets being signed
+            upper = (upper + 1) % 0x10000
+        end
+        n = upper
+    end
+
+    if self.negate or self.signed then
+        if n >= 0x10000 or n < -0x8000 then
+            return n, 'value out of range'
+        end
+        n = n % 0x10000
+    end
+
+    return n
+end
+
 return Token
diff --git a/lips/overrides.lua b/lips/overrides.lua
index e7ac500..d6adf32 100644
--- a/lips/overrides.lua
+++ b/lips/overrides.lua
@@ -16,7 +16,11 @@ local function tob_override(self, name)
     else -- NUM or LABELSYM
         local o = self:pop('CONST')
         if self:peek('NUM') then
-            o:set('offset', self:pop('CONST').tok)
+            local temp, err = self:pop('CONST'):compute()
+            if err then
+                self:error(err, temp)
+            end
+            o:set('offset', temp)
         end
         offset = self:token(o)
         if not o.portion then