diff --git a/src/os.cpp b/src/os.cpp
index 5844070609..6c1a2581df 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -1130,7 +1130,7 @@ Error os_get_cwd(Buf *out_cwd) {
 bool ATTRIBUTE_MUST_USE os_is_cygwin_pty(int fd) {
 #if defined(ZIG_OS_WINDOWS)
     HANDLE handle = (HANDLE)_get_osfhandle(fd);
-    
+
     // Cygwin/msys's pty is a pipe.
     if (handle == INVALID_HANDLE_VALUE || GetFileType(handle) != FILE_TYPE_PIPE) {
         return false;
@@ -1138,7 +1138,7 @@ bool ATTRIBUTE_MUST_USE os_is_cygwin_pty(int fd) {
 
     int size = sizeof(FILE_NAME_INFO) + sizeof(WCHAR) * MAX_PATH;
     WCHAR *p = NULL;
-    
+
     FILE_NAME_INFO *nameinfo = (FILE_NAME_INFO *)allocate<char>(size);
     if (nameinfo == NULL) {
         return false;
@@ -1179,13 +1179,13 @@ bool ATTRIBUTE_MUST_USE os_is_cygwin_pty(int fd) {
     free(nameinfo);
     return (p != NULL);
 #else
-    return false
+    return false;
 #endif
 }
 
 bool os_stderr_tty(void) {
 #if defined(ZIG_OS_WINDOWS)
-    return _isatty(_fileno(stderr)) != 0 || os_is_cygwin_pty(_fileno(stderr));
+    return _isatty(fileno(stderr)) != 0 || os_is_cygwin_pty(fileno(stderr));
 #elif defined(ZIG_OS_POSIX)
     return isatty(STDERR_FILENO) != 0;
 #else
diff --git a/src/os.hpp b/src/os.hpp
index fc0e1929f2..7354528c34 100644
--- a/src/os.hpp
+++ b/src/os.hpp
@@ -89,6 +89,11 @@ struct Termination {
 #define OsFile int
 #endif
 
+#if defined(ZIG_OS_WINDOWS)
+#undef fileno
+#define fileno _fileno
+#endif
+
 struct OsTimeStamp {
     uint64_t sec;
     uint64_t nsec;
diff --git a/src/target.cpp b/src/target.cpp
index d34254f1d1..695a810e39 100644
--- a/src/target.cpp
+++ b/src/target.cpp
@@ -1507,7 +1507,7 @@ bool target_is_single_threaded(const ZigTarget *target) {
 static ZigLLVM_EnvironmentType target_get_win32_abi() {
     FILE* files[] = { stdin, stdout, stderr, nullptr };
     for (int i = 0; files[i] != nullptr; i++) {
-        if (os_is_cygwin_pty(_fileno(files[i]))) {
+        if (os_is_cygwin_pty(fileno(files[i]))) {
             return ZigLLVM_GNU;
         }
     }
diff --git a/std/os/windows.zig b/std/os/windows.zig
index ac76e8f58f..954e56443f 100644
--- a/std/os/windows.zig
+++ b/std/os/windows.zig
@@ -65,7 +65,7 @@ pub const CreateFileError = error{
     InvalidUtf8,
 
     /// On Windows, file paths cannot contain these characters:
-    /// '/', '*', '?', '"', '<', '>', '|'
+    /// '*', '?', '"', '<', '>', '|', and '/' (when the ABI is not GNU)
     BadPathName,
 
     Unexpected,
@@ -831,8 +831,8 @@ pub fn sliceToPrefixedSuffixedFileW(s: []const u8, comptime suffix: []const u16)
     // disallow forward slashes in zig std lib file functions on Windows.
     for (s) |byte| {
         switch (byte) {
-            '/', '*', '?', '"', '<', '>', '|' => return error.BadPathName,
-            else => {},
+            '*', '?', '"', '<', '>', '|' => return error.BadPathName,
+            else => if (builtin.abi == .msvc and byte == '/') return error.BadPathName,
         }
     }
     const start_index = if (mem.startsWith(u8, s, "\\\\") or !std.fs.path.isAbsolute(s)) 0 else blk: {
@@ -866,7 +866,6 @@ pub fn unexpectedError(err: DWORD) std.os.UnexpectedError {
     return error.Unexpected;
 }
 
-
 /// Call this when you made a windows NtDll call
 /// and you get an unexpected status.
 pub fn unexpectedStatus(status: NTSTATUS) std.os.UnexpectedError {