diff --git a/lib/system/alloc.nim b/lib/system/alloc.nim
index d4c686869..47e3318fd 100644
--- a/lib/system/alloc.nim
+++ b/lib/system/alloc.nim
@@ -38,7 +38,7 @@ type
   Trunk = object
     next: PTrunk         # all nodes are connected with this pointer
     key: int             # start address at bit 0
-    bits: array[0..IntsPerTrunk-1, int] # a bit vector
+    bits: array[0..IntsPerTrunk-1, uint] # a bit vector
 
   TrunkBuckets = array[0..255, PTrunk]
   IntSet = object
@@ -332,21 +332,21 @@ proc contains(s: IntSet, key: int): bool =
   var t = intSetGet(s, key shr TrunkShift)
   if t != nil:
     var u = key and TrunkMask
-    result = (t.bits[u shr IntShift] and (1 shl (u and IntMask))) != 0
+    result = (t.bits[u shr IntShift] and (uint(1) shl (u and IntMask))) != 0
   else:
     result = false
 
 proc incl(a: var MemRegion, s: var IntSet, key: int) =
   var t = intSetPut(a, s, key shr TrunkShift)
   var u = key and TrunkMask
-  t.bits[u shr IntShift] = t.bits[u shr IntShift] or (1 shl (u and IntMask))
+  t.bits[u shr IntShift] = t.bits[u shr IntShift] or (uint(1) shl (u and IntMask))
 
 proc excl(s: var IntSet, key: int) =
   var t = intSetGet(s, key shr TrunkShift)
   if t != nil:
     var u = key and TrunkMask
     t.bits[u shr IntShift] = t.bits[u shr IntShift] and not
-        (1 shl (u and IntMask))
+        (uint(1) shl (u and IntMask))
 
 iterator elements(t: IntSet): int {.inline.} =
   # while traversing it is forbidden to change the set!
diff --git a/lib/system/cellsets.nim b/lib/system/cellsets.nim
index d56de06bb..7712681bc 100644
--- a/lib/system/cellsets.nim
+++ b/lib/system/cellsets.nim
@@ -27,7 +27,7 @@ type
   BitIndex = range[0..UnitsPerPage-1]
   PageDesc {.final, pure.} = object
     next: PPageDesc # all nodes are connected with this pointer
-    key: ByteAddress   # start address at bit 0
+    key: uint   # start address at bit 0
     bits: array[BitIndex, int] # a bit vector
 
   PPageDescArray = ptr UncheckedArray[PPageDesc]
@@ -97,7 +97,7 @@ proc nextTry(h, maxHash: int): int {.inline.} =
   # generates each int in range(maxHash) exactly once (see any text on
   # random-number generation for proof).
 
-proc cellSetGet(t: CellSet, key: ByteAddress): PPageDesc =
+proc cellSetGet(t: CellSet, key: uint): PPageDesc =
   var h = cast[int](key) and t.max
   while t.data[h] != nil:
     if t.data[h].key == key: return t.data[h]
@@ -122,7 +122,7 @@ proc cellSetEnlarge(t: var CellSet) =
   dealloc(t.data)
   t.data = n
 
-proc cellSetPut(t: var CellSet, key: ByteAddress): PPageDesc =
+proc cellSetPut(t: var CellSet, key: uint): PPageDesc =
   var h = cast[int](key) and t.max
   while true:
     var x = t.data[h]
@@ -146,33 +146,33 @@ proc cellSetPut(t: var CellSet, key: ByteAddress): PPageDesc =
 # ---------- slightly higher level procs --------------------------------------
 
 proc contains(s: CellSet, cell: PCell): bool =
-  var u = cast[ByteAddress](cell)
+  var u = cast[uint](cell)
   var t = cellSetGet(s, u shr PageShift)
   if t != nil:
-    u = (u %% PageSize) /% MemAlign
+    u = (u mod PageSize) div MemAlign
     result = (t.bits[u shr IntShift] and (1 shl (u and IntMask))) != 0
   else:
     result = false
 
 proc incl(s: var CellSet, cell: PCell) {.noinline.} =
-  var u = cast[ByteAddress](cell)
+  var u = cast[uint](cell)
   var t = cellSetPut(s, u shr PageShift)
-  u = (u %% PageSize) /% MemAlign
+  u = (u mod PageSize) div MemAlign
   t.bits[u shr IntShift] = t.bits[u shr IntShift] or (1 shl (u and IntMask))
 
 proc excl(s: var CellSet, cell: PCell) =
-  var u = cast[ByteAddress](cell)
+  var u = cast[uint](cell)
   var t = cellSetGet(s, u shr PageShift)
   if t != nil:
-    u = (u %% PageSize) /% MemAlign
+    u = (u mod PageSize) div MemAlign
     t.bits[u shr IntShift] = (t.bits[u shr IntShift] and
                               not (1 shl (u and IntMask)))
 
 proc containsOrIncl(s: var CellSet, cell: PCell): bool =
-  var u = cast[ByteAddress](cell)
+  var u = cast[uint](cell)
   var t = cellSetGet(s, u shr PageShift)
   if t != nil:
-    u = (u %% PageSize) /% MemAlign
+    u = (u mod PageSize) div MemAlign
     result = (t.bits[u shr IntShift] and (1 shl (u and IntMask))) != 0
     if not result:
       t.bits[u shr IntShift] = t.bits[u shr IntShift] or
@@ -185,15 +185,15 @@ iterator elements(t: CellSet): PCell {.inline.} =
   # while traversing it is forbidden to add pointers to the tree!
   var r = t.head
   while r != nil:
-    var i = 0
-    while i <= high(r.bits):
+    var i: uint = 0
+    while int(i) <= high(r.bits):
       var w = r.bits[i] # taking a copy of r.bits[i] here is correct, because
       # modifying operations are not allowed during traversation
-      var j = 0
+      var j: uint = 0
       while w != 0:         # test all remaining bits for zero
         if (w and 1) != 0:  # the bit is set!
           yield cast[PCell]((r.key shl PageShift) or
-                              (i shl IntShift +% j) *% MemAlign)
+                              (i shl IntShift + j) * MemAlign)
         inc(j)
         w = w shr 1
       inc(i)
@@ -238,16 +238,16 @@ iterator elementsExcept(t, s: CellSet): PCell {.inline.} =
   var r = t.head
   while r != nil:
     let ss = cellSetGet(s, r.key)
-    var i = 0
-    while i <= high(r.bits):
+    var i:uint = 0
+    while int(i) <= high(r.bits):
       var w = r.bits[i]
       if ss != nil:
         w = w and not ss.bits[i]
-      var j = 0
+      var j:uint = 0
       while w != 0:
         if (w and 1) != 0:
           yield cast[PCell]((r.key shl PageShift) or
-                              (i shl IntShift +% j) *% MemAlign)
+                              (i shl IntShift + j) * MemAlign)
         inc(j)
         w = w shr 1
       inc(i)
diff --git a/lib/system/gc.nim b/lib/system/gc.nim
index db5371156..397708ca3 100644
--- a/lib/system/gc.nim
+++ b/lib/system/gc.nim
@@ -133,7 +133,7 @@ proc extGetCellType(c: pointer): PNimType {.compilerproc.} =
   result = usrToCell(c).typ
 
 proc internRefcount(p: pointer): int {.exportc: "getRefcount".} =
-  result = int(usrToCell(p).refcount) shr rcShift
+  result = usrToCell(p).refcount shr rcShift
 
 # this that has to equals zero, otherwise we have to round up UnitsPerPage:
 when BitsPerPage mod (sizeof(int)*8) != 0:
diff --git a/lib/system/strmantle.nim b/lib/system/strmantle.nim
index 8ff2e0ee0..457e0eab5 100644
--- a/lib/system/strmantle.nim
+++ b/lib/system/strmantle.nim
@@ -30,15 +30,15 @@ proc eqStrings(a, b: string): bool {.inline, compilerProc.} =
 proc hashString(s: string): int {.compilerproc.} =
   # the compiler needs exactly the same hash function!
   # this used to be used for efficient generation of string case statements
-  var h = 0
+  var h : uint = 0
   for i in 0..len(s)-1:
-    h = h +% ord(s[i])
-    h = h +% h shl 10
+    h = h + uint(s[i])
+    h = h + h shl 10
     h = h xor (h shr 6)
-  h = h +% h shl 3
+  h = h + h shl 3
   h = h xor (h shr 11)
-  h = h +% h shl 15
-  result = h
+  h = h + h shl 15
+  result = cast[int](h)
 
 proc addInt*(result: var string; x: int64) =
   ## Converts integer to its string representation and appends it to `result`.