diff --git a/core/alien/c-types/c-types.factor b/core/alien/c-types/c-types.factor
index 405d679f4a..c553ca5cfb 100755
--- a/core/alien/c-types/c-types.factor
+++ b/core/alien/c-types/c-types.factor
@@ -151,8 +151,9 @@ M: byte-array byte-length length ;
     swap dup length memcpy ;
 
 : (define-nth) ( word type quot -- )
-    >r heap-size [ rot * >fixnum ] swap prefix
-    r> append define-inline ;
+    [
+        \ swap , [ heap-size , [ * >fixnum ] % ] [ % ] bi*
+    ] [ ] make define-inline ;
 
 : nth-word ( name vocab -- word )
     >r "-nth" append r> create ;
diff --git a/core/optimizer/math/math.factor b/core/optimizer/math/math.factor
index c20cba99cb..2c4e33e183 100755
--- a/core/optimizer/math/math.factor
+++ b/core/optimizer/math/math.factor
@@ -406,7 +406,7 @@ most-negative-fixnum most-positive-fixnum [a,b]
 
 : convert-mod-to-and ( #call -- node )
     dup
-    dup node-in-d second node-literal 1-
+    dup in-d>> second node-literal 1-
     [ nip bitand ] curry f splice-quot ;
 
 \ mod [
@@ -438,6 +438,19 @@ most-negative-fixnum most-positive-fixnum [a,b]
     }
 } define-optimizers
 
+: convert-*-to-shift? ( #call -- ? )
+    dup in-d>> second node-literal
+    dup integer? [ power-of-2? ] [ drop f ] if ;
+
+: convert-*-to-shift ( #call -- ? )
+    dup dup in-d>> second node-literal log2
+    [ nip fixnum-shift-fast ] curry
+    f splice-quot ;
+
+\ fixnum*fast {
+    { [ dup convert-*-to-shift? ] [ convert-*-to-shift ] }
+} define-optimizers
+
 { + - * / }
 [ { number number } "input-classes" set-word-prop ] each