diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 19ef8a1177..7cde101cbb 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -900,6 +900,8 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
       if sameDistinctTypes(f, a): result = isEqual
       elif f.base.kind == tyAnything: result = isGeneric
       elif c.coerceDistincts: result = typeRel(c, f.base, a)
+    elif a.kind == tyNil and f.base.kind in NilableTypes:
+      result = f.allowsNil
     elif c.coerceDistincts: result = typeRel(c, f.base, a)
   of tySet:
     if a.kind == tySet:
diff --git a/lib/pure/math.nim b/lib/pure/math.nim
index c088e3d7dc..58d9879b20 100644
--- a/lib/pure/math.nim
+++ b/lib/pure/math.nim
@@ -219,7 +219,7 @@ when not defined(JS):
     ##
     ## .. code-block:: nim
     ##  echo ceil(-2.1) ## -2.0
-  
+
   when defined(windows) and defined(vcc):
     proc round0[T: float32|float64](x: T): T =
       ## Windows compilers prior to MSVC 2012 do not implement 'round',
@@ -360,7 +360,7 @@ proc `mod`*[T: float32|float64](x, y: T): T =
 proc `^`*[T](x, y: T): T =
   ## Computes ``x`` to the power ``y`. ``x`` must be non-negative, use
   ## `pow <#pow,float,float>` for negative exponents.
-  assert y >= 0
+  assert y >= T(0)
   var (x, y) = (x, y)
   result = 1
 
diff --git a/lib/pure/memfiles.nim b/lib/pure/memfiles.nim
index ff3e74d59f..aa32778c52 100644
--- a/lib/pure/memfiles.nim
+++ b/lib/pure/memfiles.nim
@@ -42,6 +42,10 @@ type
 
 proc mapMem*(m: var MemFile, mode: FileMode = fmRead,
              mappedSize = -1, offset = 0): pointer =
+  ## returns a pointer to a mapped portion of MemFile `m`
+  ##
+  ## ``mappedSize`` of ``-1`` maps to the whole file, and
+  ## ``offset`` must be multiples of the PAGE SIZE of your OS
   var readonly = mode == fmRead
   when defined(windows):
     result = mapViewOfFileEx(
@@ -68,7 +72,9 @@ proc mapMem*(m: var MemFile, mode: FileMode = fmRead,
 proc unmapMem*(f: var MemFile, p: pointer, size: int) =
   ## unmaps the memory region ``(p, <p+size)`` of the mapped file `f`.
   ## All changes are written back to the file system, if `f` was opened
-  ## with write access. ``size`` must be of exactly the size that was requested
+  ## with write access.
+  ##
+  ## ``size`` must be of exactly the size that was requested
   ## via ``mapMem``.
   when defined(windows):
     if unmapViewOfFile(p) == 0: raiseOSError(osLastError())
@@ -79,9 +85,17 @@ proc unmapMem*(f: var MemFile, p: pointer, size: int) =
 proc open*(filename: string, mode: FileMode = fmRead,
            mappedSize = -1, offset = 0, newFileSize = -1): MemFile =
   ## opens a memory mapped file. If this fails, ``EOS`` is raised.
-  ## `newFileSize` can only be set if the file does not exist and is opened
-  ## with write access (e.g., with fmReadWrite). `mappedSize` and `offset`
-  ## can be used to map only a slice of the file. Example:
+  ##
+  ## ``newFileSize`` can only be set if the file does not exist and is opened
+  ## with write access (e.g., with fmReadWrite).
+  ##
+  ##``mappedSize`` and ``offset``
+  ## can be used to map only a slice of the file.
+  ##
+  ## ``offset`` must be multiples of the PAGE SIZE of your OS
+  ## (usually 4K or 8K but is unique to your OS)
+  ##
+  ## Example:
   ##
   ## .. code-block:: nim
   ##   var
@@ -285,7 +299,9 @@ iterator memSlices*(mfile: MemFile, delim='\l', eat='\r'): MemSlice {.inline.} =
   ## iterate over line-like records in a file.  However, returned (data,size)
   ## objects are not Nim strings, bounds checked Nim arrays, or even terminated
   ## C strings.  So, care is required to access the data (e.g., think C mem*
-  ## functions, not str* functions).  Example:
+  ## functions, not str* functions).
+  ##
+  ## Example:
   ##
   ## .. code-block:: nim
   ##   var count = 0
@@ -318,7 +334,9 @@ iterator lines*(mfile: MemFile, buf: var TaintedString, delim='\l', eat='\r'): T
   ## Replace contents of passed buffer with each new line, like
   ## `readLine(File) <system.html#readLine,File,TaintedString>`_.
   ## `delim`, `eat`, and delimiting logic is exactly as for
-  ## `memSlices <#memSlices>`_, but Nim strings are returned.  Example:
+  ## `memSlices <#memSlices>`_, but Nim strings are returned.
+  ##
+  ## Example:
   ##
   ## .. code-block:: nim
   ##   var buffer: TaintedString = ""
@@ -335,7 +353,9 @@ iterator lines*(mfile: MemFile, delim='\l', eat='\r'): TaintedString {.inline.}
   ## Return each line in a file as a Nim string, like
   ## `lines(File) <system.html#lines.i,File>`_.
   ## `delim`, `eat`, and delimiting logic is exactly as for
-  ## `memSlices <#memSlices>`_, but Nim strings are returned.  Example:
+  ## `memSlices <#memSlices>`_, but Nim strings are returned.
+  ##
+  ## Example:
   ##
   ## .. code-block:: nim
   ##   for line in lines(memfiles.open("foo")):
diff --git a/tests/distinct/tnil.nim b/tests/distinct/tnil.nim
new file mode 100644
index 0000000000..ed0ac995a0
--- /dev/null
+++ b/tests/distinct/tnil.nim
@@ -0,0 +1,47 @@
+discard """
+  file: "tnil.nim"
+  output: '''0x1
+
+nil
+
+nil
+
+'''
+"""
+
+type
+  MyPointer = distinct pointer
+  MyString = distinct string
+  MyStringNotNil = distinct (string not nil)
+  MyInt = distinct int
+
+proc foo(a: MyPointer) =
+  echo a.repr
+
+foo(cast[MyPointer](1))
+foo(cast[MyPointer](nil))
+foo(nil)
+
+var p: MyPointer
+p = cast[MyPointer](1)
+p = cast[MyPointer](nil)
+p = nil.MyPointer
+p = nil
+
+var c: MyString
+c = "Test".MyString
+c = nil.MyString
+c = nil
+
+p = nil
+doAssert(compiles(c = p) == false)
+
+var n: MyStringNotNil = "Test".MyStringNotNil # Cannot prove warning ...
+n = "Test".MyStringNotNil
+doAssert(compiles(n = nil.MyStringNotNil) == false)
+doAssert(compiles(n = nil.MyStringNotNil) == false)
+doAssert(compiles(n = nil) == false)
+
+var i: MyInt
+i = 1.MyInt
+doAssert(compiles(i = nil) == false)