diff --git a/ueforth/common/boot.fs b/ueforth/common/boot.fs
index 6f9a919..8a1b090 100644
--- a/ueforth/common/boot.fs
+++ b/ueforth/common/boot.fs
@@ -137,7 +137,7 @@ defer bye
 variable hld
 : pad ( -- a ) here 80 + ;
 : digit ( u -- c ) 9 over < 7 and + 48 + ;
-: extract ( n base -- n c ) 0 swap um/mod swap digit ;
+: extract ( n base -- n c ) u/mod swap digit ;
 : <# ( -- ) pad hld ! ;
 : hold ( c -- ) hld @ 1 - dup hld ! c! ;
 : # ( u -- u ) base @ extract hold ;
diff --git a/ueforth/common/opcodes.h b/ueforth/common/opcodes.h
index c611d8e..f8c3ad9 100644
--- a/ueforth/common/opcodes.h
+++ b/ueforth/common/opcodes.h
@@ -19,10 +19,7 @@ typedef uint64_t udcell_t;
 #define COMMA(n) *g_sys.heap++ = (n)
 #define IMMEDIATE() g_sys.last[-1] |= 1
 #define DOES(ip) *g_sys.last = (cell_t) && OP_DODOES; g_sys.last[1] = (cell_t) ip
-#ifndef UMSMOD_FUNC
-#define UMSMOD_FUNC udcell_t ud = *(udcell_t *) &sp[-1]; \
-                    --sp; *sp = (cell_t) (ud % tos); \
-                    tos = (cell_t) (ud / tos)
+#ifndef SSMOD_FUNC
 #define SSMOD_FUNC dcell_t d = (dcell_t) *sp * (dcell_t) sp[-1]; \
                    --sp; *sp = (cell_t) (((udcell_t) d) % tos); \
                    tos = (cell_t) (d < 0 ? ~(~d / tos) : d / tos)
@@ -33,7 +30,8 @@ typedef uint64_t udcell_t;
   X("0=", ZEQUAL, tos = !tos ? -1 : 0) \
   X("0<", ZLESS, tos = (tos|0) < 0 ? -1 : 0) \
   X("+", PLUS, tos = (tos + *sp) | 0; --sp) \
-  X("UM/MOD", UMSMOD, UMSMOD_FUNC) \
+  X("U/MOD", USMOD, w = *sp; *sp = (uintptr_t) w % (uintptr_t) tos; \
+                    tos = (uintptr_t) w / tos) \
   X("*/MOD", SSMOD, SSMOD_FUNC) \
   X("AND", AND, tos = tos & *sp; --sp) \
   X("OR", OR, tos = tos | *sp; --sp) \
diff --git a/ueforth/web/fuse_web.js b/ueforth/web/fuse_web.js
index 544c2f2..06e5430 100755
--- a/ueforth/web/fuse_web.js
+++ b/ueforth/web/fuse_web.js
@@ -43,7 +43,6 @@ cases = ReplaceAll(cases, '&g_sys', 'g_sys');
 cases = ReplaceAll(cases, '&& OP_DOCOLON', '0');
 cases = ReplaceAll(cases, '&& OP_DOCREATE', '1');
 cases = ReplaceAll(cases, 'goto **(void **) w', 'break decode');
-cases = ReplaceAll(cases, 'UMSMOD', '');
 cases = ReplaceAll(cases, 'SSMOD', '');
 
 code = code.replace('{{boot}}', function() { return boot; });
diff --git a/ueforth/web/web.template.js b/ueforth/web/web.template.js
index f342d12..4c2d1b4 100644
--- a/ueforth/web/web.template.js
+++ b/ueforth/web/web.template.js
@@ -42,7 +42,6 @@ function VM(stdlib, foreign, heap) {
 
   var imul = stdlib.Math.imul;
 
-  var UMSMOD = foreign.UMSMOD;
   var SSMOD = foreign.SSMOD;
   var Call = foreign.Call;
   var COMMA = foreign.COMMA;
@@ -102,7 +101,6 @@ var ffi = {
   create: function() {},
   parse: function() {},
   COMMA: function() {},
-  UMSMOD: function() {},
   SSMOD: function() {},
   DOES: function() {},
   IMMEDIATE: function() {},
diff --git a/ueforth/windows/windows_main.c b/ueforth/windows/windows_main.c
index eb3b844..086c8e7 100644
--- a/ueforth/windows/windows_main.c
+++ b/ueforth/windows/windows_main.c
@@ -2,11 +2,6 @@
 
 #define CALLTYPE WINAPI
 
-# define UMSMOD_FUNC \
-  asm("div %2" \
-      : "=a" (tos), "=d" (sp[-1]) \
-      : "r" (tos), "a" (sp[-1]), "d" (*sp)); --sp
-
 # define SSMOD_FUNC \
   w = tos; asm("imul %4\n\t" \
       "idiv %2" \