diff --git a/nimterop/cimport.nim b/nimterop/cimport.nim
index 1f82b6f..86cf43a 100644
--- a/nimterop/cimport.nim
+++ b/nimterop/cimport.nim
@@ -42,7 +42,7 @@ proc walkDirImpl(indir, inext: string, file=true): seq[string] =
     dir = joinPathIfRel(getProjectPath(), indir)
     ext =
       if inext.len != 0:
-        when not defined(Windows):
+        if buildOS != "windows":
           "-name " & inext
         else:
           "\\" & inext
@@ -51,7 +51,7 @@ proc walkDirImpl(indir, inext: string, file=true): seq[string] =
 
   let
     cmd =
-      when defined(Windows):
+      if buildOS == "windows":
         if file:
           "cmd /c dir /s/b/a-d " & dir.replace("/", "\\") & ext
         else:
@@ -70,13 +70,17 @@ proc walkDirImpl(indir, inext: string, file=true): seq[string] =
 proc getFileDate(fullpath: string): string =
   var
     ret = 0
-    cmd =
-      when defined(Windows):
-        &"cmd /c for %a in ({fullpath.quoteShell}) do echo %~ta"
-      elif defined(Linux):
-        &"stat -c %y {fullpath.quoteShell}"
-      elif defined(OSX):
-        &"stat -f %m {fullpath.quoteShell}"
+    cmd = ""
+
+  case buildOS
+  of "windows":
+    cmd = &"cmd /c for %a in ({fullpath.quoteShell}) do echo %~ta"
+  of "linux":
+    cmd = &"stat -c %y {fullpath.quoteShell}"
+  of "macosx":
+    cmd = &"stat -f %m {fullpath.quoteShell}"
+  else:
+    doAssert false
 
   (result, ret) = gorgeEx(cmd)
 
@@ -115,7 +119,7 @@ proc getNimCheckError(output: string): tuple[tmpFile, errors: string] =
 proc getToast(fullpath: string, recurse: bool = false): string =
   var
     ret = 0
-    cmd = when defined(Windows): "cmd /c " else: ""
+    cmd = if buildOS == "windows": "cmd /c " else: ""
 
   let toastExe = toastExePath()
   doAssert fileExists(toastExe), "toast not compiled: " & toastExe.quoteShell &
@@ -146,7 +150,7 @@ proc getToast(fullpath: string, recurse: bool = false): string =
 proc getGccPaths(mode = "c"): string =
   var
     ret = 0
-    nul = when defined(Windows): "nul" else: "/dev/null"
+    nul = if buildOS == "windows": "nul" else: "/dev/null"
     mmode = if mode == "cpp": "c++" else: mode
 
   (result, ret) = gorgeEx("gcc -Wp,-v -x" & mmode & " " & nul)
@@ -452,7 +456,7 @@ macro cCompile*(path: static string, mode = "c", exclude = ""): untyped =
       if mode.strVal().contains("cpp"):
         for i in @["*.cpp", "*.c++", "*.cc", "*.cxx"]:
           stmt &= dcompile(fpath, exclude.strVal(), i)
-        when not defined(Windows):
+        if buildOS != "windows":
           stmt &= dcompile(fpath, exclude.strVal(), "*.C")
       else:
         stmt &= dcompile(fpath, exclude.strVal(), "*.c")
diff --git a/nimterop/git.nim b/nimterop/git.nim
index b0380c2..6dbf468 100644
--- a/nimterop/git.nim
+++ b/nimterop/git.nim
@@ -2,11 +2,14 @@ import macros, os, osproc, regex, strformat, strutils
 
 import "."/[paths, compat]
 
+when not defined(buildOS):
+  const buildOS* {.magic: "BuildOS".} = ""
+
 proc execAction*(cmd: string, nostderr=false): string =
   var
     ccmd = ""
     ret = 0
-  when defined(Windows):
+  when buildOS == "windows":
     ccmd = "cmd /c " & cmd
   elif defined(posix):
     ccmd = cmd
@@ -23,7 +26,7 @@ proc execAction*(cmd: string, nostderr=false): string =
 proc mkDir*(dir: string) =
   if not dirExists(dir):
     let
-      flag = when not defined(Windows): "-p" else: ""
+      flag = if buildOS != "windows": "-p" else: ""
     discard execAction(&"mkdir {flag} {dir.quoteShell}")
 
 proc cpFile*(source, dest: string, move=false) =
@@ -31,7 +34,7 @@ proc cpFile*(source, dest: string, move=false) =
     source = source.replace("/", $DirSep)
     dest = dest.replace("/", $DirSep)
     cmd =
-      when defined(Windows):
+      if buildOS == "windows":
         if move:
           "move /y"
         else:
@@ -49,7 +52,7 @@ proc mvFile*(source, dest: string) =
 
 proc extractZip*(zipfile, outdir: string) =
   var cmd = "unzip -o $#"
-  if defined(Windows):
+  if buildOS == "windows":
     cmd = "powershell -nologo -noprofile -command \"& { Add-Type -A " &
           "'System.IO.Compression.FileSystem'; " &
           "[IO.Compression.ZipFile]::ExtractToDirectory('$#', '.'); }\""
@@ -65,7 +68,7 @@ proc downloadUrl*(url, outdir: string) =
   if not (ext == ".zip" and fileExists(outdir/file)):
     echo "Downloading " & file
     mkDir(outdir)
-    var cmd = if defined(Windows):
+    var cmd = if buildOS == "windows":
       "powershell [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12; wget $# -OutFile $#"
     else:
       "curl $# -o $#"