diff --git a/lib/pure/os.nim b/lib/pure/os.nim
index 60ade511afcbd..f8497bf17620a 100644
--- a/lib/pure/os.nim
+++ b/lib/pure/os.nim
@@ -1654,22 +1654,19 @@ proc isAdmin*: bool {.noWeirdTarget.} =
   when defined(windows):
     # Rewrite of the example from Microsoft Docs:
     # https://docs.microsoft.com/en-us/windows/win32/api/securitybaseapi/nf-securitybaseapi-checktokenmembership#examples
-    var b: WINBOOL
-    var ntAuthority = SID_IDENTIFIER_AUTHORITY(value: [
-      BYTE(0), BYTE(0), BYTE(0), BYTE(0), BYTE(0), BYTE(SECURITY_NT_AUTHORITY)
-    ])
+    var ntAuthority = SID_IDENTIFIER_AUTHORITY(Value: SECURITY_NT_AUTHORITY)
     var administratorsGroup: PSID
-    b = AllocateAndInitializeSid(addr ntAuthority,
-                                 BYTE(2),
-                                 SECURITY_BUILTIN_DOMAIN_RID,
-                                 DOMAIN_ALIAS_RID_ADMINS,
-                                 0, 0, 0, 0, 0, 0,
-                                 addr administratorsGroup)
-    if bool(b):
-      if not bool(CheckTokenMembership(0, administratorsGroup, addr b)):
+    var b: WINBOOL = AllocateAndInitializeSid(addr ntAuthority,
+                                              BYTE(2),
+                                              SECURITY_BUILTIN_DOMAIN_RID,
+                                              DOMAIN_ALIAS_RID_ADMINS,
+                                              0, 0, 0, 0, 0, 0,
+                                              addr administratorsGroup)
+    if isSuccess(b):
+      if not isSuccess(CheckTokenMembership(0, administratorsGroup, addr b)):
         b = 0
       discard FreeSid(administratorsGroup)
-    return bool(b)
+    return isSuccess(b)
   else:
     return geteuid() == 0
 
diff --git a/lib/windows/winlean.nim b/lib/windows/winlean.nim
index 3800e99bf88d4..1c07b54c866b8 100644
--- a/lib/windows/winlean.nim
+++ b/lib/windows/winlean.nim
@@ -139,6 +139,7 @@ const
 
   HANDLE_FLAG_INHERIT* = 0x00000001'i32
 
+proc isSuccess*(a: WINBOOL): bool {.inline.} = a != 0
 proc getVersionExW*(lpVersionInfo: ptr OSVERSIONINFO): WINBOOL {.
     stdcall, dynlib: "kernel32", importc: "GetVersionExW", sideEffect.}
 proc getVersionExA*(lpVersionInfo: ptr OSVERSIONINFO): WINBOOL {.
@@ -1133,19 +1134,20 @@ proc setFileTime*(hFile: Handle, lpCreationTime: LPFILETIME,
      {.stdcall, dynlib: "kernel32", importc: "SetFileTime".}
 
 type
-  SID_IDENTIFIER_AUTHORITY* = object
-    value*: array[6, BYTE]
-  PSID_IDENTIFIER_AUTHORITY* = ptr SID_IDENTIFIER_AUTHORITY
-  SID* = object
-    revision: BYTE
-    subAuthorityCount: BYTE
-    identifierAuthority: SID_IDENTIFIER_AUTHORITY
-    subAuthority: ptr ptr DWORD
-  PSID* = ptr SID
+  SID_IDENTIFIER_AUTHORITY* {.importc, header: "windows.h".} = object
+    Value*: array[6, BYTE]
+  PSID_IDENTIFIER_AUTHORITY* {.importc, header: "windows.h".} = ptr SID_IDENTIFIER_AUTHORITY
+  SID* {.importc, header: "windows.h".} = object
+    Revision: BYTE
+    SubAuthorityCount: BYTE
+    IdentifierAuthority: SID_IDENTIFIER_AUTHORITY
+    SubAuthority: ptr ptr DWORD
+  PSID* {.importc, header: "windows.h".} = ptr SID
 
 const
   # https://docs.microsoft.com/en-us/windows/win32/secauthz/sid-components
-  SECURITY_NT_AUTHORITY* = 5
+  # https://github.com/mirror/mingw-w64/blob/84c950bdab7c999ace49fe8383856be77f88c4a8/mingw-w64-headers/include/winnt.h#L2994
+  SECURITY_NT_AUTHORITY* = [BYTE(0), BYTE(0), BYTE(0), BYTE(0), BYTE(0), BYTE(5)]
   SECURITY_BUILTIN_DOMAIN_RID* = 32
   DOMAIN_ALIAS_RID_ADMINS* = 544
 
diff --git a/tests/stdlib/tos.nim b/tests/stdlib/tos.nim
index f35c5c5aec358..76212c47253a6 100644
--- a/tests/stdlib/tos.nim
+++ b/tests/stdlib/tos.nim
@@ -653,5 +653,5 @@ block: # normalizeExe
     doAssert "foo".dup(normalizeExe) == "foo"
 
 block: # isAdmin
-  let isAzure = existsEnv("TF_BUILD") # xxx factor with testament.specs.isAzure
+  let isAzure = defined(windows) and existsEnv("TF_BUILD") # xxx factor with testament.specs.isAzure
   if isAzure: doAssert isAdmin()