diff --git a/src/iscygpty.c b/src/iscygpty.c
new file mode 100644
index 0000000..4a6dc3d
--- /dev/null
+++ b/src/iscygpty.c
@@ -0,0 +1,181 @@
+/*
+ * iscygpty.c -- part of ptycheck
+ * https://github.com/k-takata/ptycheck
+ *
+ * Copyright (c) 2015-2016 K.Takata
+ *
+ * You can redistribute it and/or modify it under the terms of either
+ * the MIT license (as described below) or the Vim license.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <ctype.h>
+#include <io.h>
+#include <wchar.h>
+#include <windows.h>
+
+#ifdef USE_FILEEXTD
+/* VC 7.1 or earlier doesn't support SAL. */
+# if !defined(_MSC_VER) || (_MSC_VER < 1400)
+#  define __out
+#  define __in
+#  define __in_opt
+# endif
+/* Win32 FileID API Library:
+ * http://www.microsoft.com/en-us/download/details.aspx?id=22599
+ * Needed for WinXP. */
+# include <fileextd.h>
+#else /* USE_FILEEXTD */
+/* VC 8 or earlier. */
+# if defined(_MSC_VER) && (_MSC_VER < 1500)
+#  ifdef ENABLE_STUB_IMPL
+#   define STUB_IMPL
+#  else
+#   error "Win32 FileID API Library is required for VC2005 or earlier."
+#  endif
+# endif
+#endif /* USE_FILEEXTD */
+
+
+#include "iscygpty.h"
+
+//#define USE_DYNFILEID
+#ifdef USE_DYNFILEID
+typedef BOOL (WINAPI *pfnGetFileInformationByHandleEx)(
+		HANDLE					  hFile,
+		FILE_INFO_BY_HANDLE_CLASS FileInformationClass,
+		LPVOID					  lpFileInformation,
+		DWORD					  dwBufferSize
+);
+static pfnGetFileInformationByHandleEx pGetFileInformationByHandleEx = NULL;
+
+# ifndef USE_FILEEXTD
+static BOOL WINAPI stub_GetFileInformationByHandleEx(
+		HANDLE					  hFile,
+		FILE_INFO_BY_HANDLE_CLASS FileInformationClass,
+		LPVOID					  lpFileInformation,
+		DWORD					  dwBufferSize
+		)
+{
+	return FALSE;
+}
+# endif
+
+static void setup_fileid_api(void)
+{
+	if (pGetFileInformationByHandleEx != NULL) {
+		return;
+	}
+	pGetFileInformationByHandleEx = (pfnGetFileInformationByHandleEx)
+		GetProcAddress(GetModuleHandle(TEXT("kernel32.dll")),
+				"GetFileInformationByHandleEx");
+	if (pGetFileInformationByHandleEx == NULL) {
+# ifdef USE_FILEEXTD
+		pGetFileInformationByHandleEx = GetFileInformationByHandleEx;
+# else
+		pGetFileInformationByHandleEx = stub_GetFileInformationByHandleEx;
+# endif
+	}
+}
+#else
+# define pGetFileInformationByHandleEx	GetFileInformationByHandleEx
+# define setup_fileid_api()
+#endif
+
+
+#define is_wprefix(s, prefix) \
+	(wcsncmp((s), (prefix), sizeof(prefix) / sizeof(WCHAR) - 1) == 0)
+
+/* Check if the fd is a cygwin/msys's pty. */
+int is_cygpty(int fd)
+{
+#ifdef STUB_IMPL
+	return 0;
+#else
+	HANDLE h;
+	int size = sizeof(FILE_NAME_INFO) + sizeof(WCHAR) * MAX_PATH;
+	FILE_NAME_INFO *nameinfo;
+	WCHAR *p = NULL;
+
+	setup_fileid_api();
+
+	h = (HANDLE) _get_osfhandle(fd);
+	if (h == INVALID_HANDLE_VALUE) {
+		return 0;
+	}
+	/* Cygwin/msys's pty is a pipe. */
+	if (GetFileType(h) != FILE_TYPE_PIPE) {
+		return 0;
+	}
+	nameinfo = malloc(size);
+	if (nameinfo == NULL) {
+		return 0;
+	}
+	/* Check the name of the pipe:
+	 * '\{cygwin,msys}-XXXXXXXXXXXXXXXX-ptyN-{from,to}-master' */
+	if (pGetFileInformationByHandleEx(h, FileNameInfo, nameinfo, size)) {
+		nameinfo->FileName[nameinfo->FileNameLength / sizeof(WCHAR)] = L'\0';
+		p = nameinfo->FileName;
+		if (is_wprefix(p, L"\\cygwin-")) {		/* Cygwin */
+			p += 8;
+		} else if (is_wprefix(p, L"\\msys-")) {	/* MSYS and MSYS2 */
+			p += 6;
+		} else {
+			p = NULL;
+		}
+		if (p != NULL) {
+			while (*p && isxdigit(*p))	/* Skip 16-digit hexadecimal. */
+				++p;
+			if (is_wprefix(p, L"-pty")) {
+				p += 4;
+			} else {
+				p = NULL;
+			}
+		}
+		if (p != NULL) {
+			while (*p && isdigit(*p))	/* Skip pty number. */
+				++p;
+			if (is_wprefix(p, L"-from-master")) {
+				//p += 12;
+			} else if (is_wprefix(p, L"-to-master")) {
+				//p += 10;
+			} else {
+				p = NULL;
+			}
+		}
+	}
+	free(nameinfo);
+	return (p != NULL);
+#endif /* STUB_IMPL */
+}
+
+/* Check if at least one cygwin/msys pty is used. */
+int is_cygpty_used(void)
+{
+	int fd, ret = 0;
+
+	for (fd = 0; fd < 3; fd++) {
+		ret |= is_cygpty(fd);
+	}
+	return ret;
+}
+
+/* vim: set ts=4 sw=4: */