diff --git a/basis/compiler/cfg/value-numbering/rewrite/rewrite.factor b/basis/compiler/cfg/value-numbering/rewrite/rewrite.factor
index 92965e40c5..988df366eb 100755
--- a/basis/compiler/cfg/value-numbering/rewrite/rewrite.factor
+++ b/basis/compiler/cfg/value-numbering/rewrite/rewrite.factor
@@ -49,9 +49,12 @@ M: insn rewrite ;
         [ src2>> tag-mask get bitand 0 = ]
     } 1&& ; inline
 
+: tagged>constant ( n -- n' )
+    tag-bits get neg shift ; inline
+
 : (rewrite-tagged-comparison) ( insn -- src1 src2 cc )
     [ src1>> vreg>expr in1>> vn>vreg ]
-    [ src2>> tag-bits get neg shift ]
+    [ src2>> tagged>constant ]
     [ cc>> ]
     tri ; inline
 
@@ -203,15 +206,20 @@ M: ##or-imm rewrite [ bitor ] \ ##or-imm combine-imm ;
 
 M: ##xor-imm rewrite [ bitxor ] \ ##xor-imm combine-imm ;
 
-: rewrite-add? ( insn -- ? )
-    src2>> vreg-small-constant? ;
-
-M: ##add rewrite
-    dup rewrite-add? [
+: new-arithmetic ( obj op -- )
+    [
         [ dst>> ]
         [ src1>> ]
-        [ src2>> vreg>constant ] tri \ ##add-imm new-insn
-        dup number-values
-    ] when ;
+        [ src2>> vreg>constant ] tri
+    ] dip new-insn dup number-values ; inline
 
-M: ##sub rewrite constant-fold ;
+: rewrite-arithmetic ( insn op -- ? )
+    over src2>> vreg-small-constant? [
+        new-arithmetic constant-fold
+    ] [
+        drop
+    ] if ; inline
+
+M: ##add rewrite \ ##add-imm rewrite-arithmetic ;
+
+M: ##sub rewrite \ ##sub-imm rewrite-arithmetic ;
diff --git a/extra/bson/bson-tests.factor b/extra/bson/bson-tests.factor
new file mode 100644
index 0000000000..e66b9c6ec2
--- /dev/null
+++ b/extra/bson/bson-tests.factor
@@ -0,0 +1,48 @@
+USING: bson.reader bson.writer byte-arrays io.encodings.binary
+io.streams.byte-array tools.test literals calendar kernel math ;
+
+IN: bson.tests
+
+: turnaround ( value -- value )
+    assoc>bv >byte-array binary [ H{ } stream>assoc ] with-byte-reader ;
+
+M: timestamp equal? ( obj1 obj2 -- ? )
+    [ timestamp>millis ] bi@ = ;
+
+[ H{ { "a" "a string" } } ] [ H{ { "a" "a string" } } turnaround ] unit-test
+
+[ H{ { "a" "a string" } { "b" H{ { "a" "a string" } } } } ]
+[ H{ { "a" "a string" } { "b" H{ { "a" "a string" } } } } turnaround ] unit-test
+
+[ H{ { "a list" { 1 2.234 "hello world" } } } ]
+[ H{ { "a list" { 1 2.234 "hello world" } } } turnaround ] unit-test
+
+[ H{ { "a quotation" [ 1 2 + ] } } ]
+[ H{ { "a quotation" [ 1 2 + ] } } turnaround ] unit-test
+
+[ H{ { "a date" T{ timestamp { year 2009 }
+                   { month 7 }
+                   { day 11 }
+                   { hour 11 }
+                   { minute 8 }
+                   { second 40+15437/200000 }
+                   { gmt-offset T{ duration { hour 2 } } } } } }
+]
+[ H{ { "a date" T{ timestamp { year 2009 }
+                   { month 7 }
+                   { day 11 }
+                   { hour 11 }
+                   { minute 8 }
+                   { second 40+15437/200000 }
+                   { gmt-offset T{ duration { hour 2 } } } } } } turnaround
+] unit-test
+                   
+[ H{ { "nested" H{ { "a" "a string" } { "b" H{ { "a" "a string" } } } } }
+     { "array" H{ { "a list" { 1 2.234 "hello world" } } } }
+     { "quot" [ 1 2 + ] } }
+]     
+[ H{ { "nested" H{ { "a" "a string" } { "b" H{ { "a" "a string" } } } } }
+     { "array" H{ { "a list" { 1 2.234 "hello world" } } } }
+     { "quot" [ 1 2 + ] } } turnaround ] unit-test
+     
+