diff --git a/base/loading.jl b/base/loading.jl
index b7b1a8524586b..8d8dc9915eab4 100644
--- a/base/loading.jl
+++ b/base/loading.jl
@@ -11,7 +11,7 @@ elseif OS_NAME == :Windows
     # GetLongPathName Win32 function returns the case-preserved filename on NTFS.
     function isfile_casesensitive(path)
         isfile(path) || return false  # Fail fast
-        longpath(path) == path
+        Filesystem.longpath(path) == path
     end
 elseif OS_NAME == :Darwin
     # HFS+ filesystem is case-preserving. The getattrlist API returns
diff --git a/base/path.jl b/base/path.jl
index 87069494faa51..6f191a0cd67c5 100644
--- a/base/path.jl
+++ b/base/path.jl
@@ -126,16 +126,15 @@ abspath(a::AbstractString, b::AbstractString...) = abspath(joinpath(a,b...))
 
 @windows_only realpath(path::AbstractString) = realpath(utf16(path))
 @windows_only function realpath(path::UTF16String)
-    p = UInt32((sizeof(path)>>2) + 1)
+    p::UInt32 = sizeof(path)>>1
     while true
-        buflength = p
-        buf = zeros(UInt16,buflength)
-        p = ccall((:GetFullPathNameW, "Kernel32"), stdcall,
+        buf = zeros(UInt16, p + 1)
+        p = ccall((:GetFullPathNameW, "kernel32"), stdcall,
             UInt32, (Cwstring, UInt32, Ptr{UInt16}, Ptr{Void}),
-            path, buflength, buf, C_NULL)
+            path, length(buf), buf, C_NULL)
         systemerror(:realpath, p == 0)
-        if (p < buflength)
-            resize!(buf, p+1)
+        if (p < length(buf))
+            resize!(buf, p + 1)
             return utf8(UTF16String(buf))
         end
     end
@@ -143,18 +142,18 @@ end
 
 @windows_only longpath(path::AbstractString) = longpath(utf16(path))
 @windows_only function longpath(path::UTF16String)
-    buf = Array(UInt16, length(path.data))
+    p::UInt32 = sizeof(path)>>1
     while true
-        p = ccall((:GetLongPathNameW, "Kernel32"), stdcall, UInt32,
+        buf = zeros(UInt16, p + 1)
+        p = ccall((:GetLongPathNameW, "kernel32"), stdcall, UInt32,
             (Cwstring, Ptr{UInt16}, UInt32),
             path, buf, length(buf))
         systemerror(:longpath, p == 0)
         # Buffer wasn't big enough, in which case `p` is the necessary buffer size
-        if (p > length(buf))
-            resize!(buf, p)
-            continue
+        if (p < length(buf))
+            resize!(buf, p + 1)
+            return utf8(UTF16String(buf))
         end
-        return utf8(UTF16String(buf))
     end
 end