diff -urN tinycc.old/libtcc.c tinycc/libtcc.c
--- tinycc.old/libtcc.c	2016-03-30 14:04:30.000000000 +0300
+++ tinycc/libtcc.c	2016-03-30 15:46:21.000000000 +0300
@@ -1508,6 +1508,96 @@
     return 0;
 }
 
+
+/* Windows stat* ( https://msdn.microsoft.com/en-us/library/14h5k7ff.aspx ):
+ * - st_gid, st_ino, st_uid: only valid on "unix" file systems (not FAT, NTFS, etc)
+ * - st_atime, st_ctime: not valid on FAT, valid on NTFS.
+ * - Other fields should be reasonably compatible (and S_ISDIR should work).
+ *
+ * BY_HANDLE_FILE_INFORMATION ( https://msdn.microsoft.com/en-us/library/windows/desktop/aa363788%28v=vs.85%29.aspx ):
+ * - File index (combined nFileIndexHigh and nFileIndexLow) _may_ change when the file is opened.
+ *   - But on NTFS: it's guaranteed to be the same value until the file is deleted.
+ * - On windows server 2012 there's a 128b file id, and the 64b one via
+ *   nFileIndex* is not guaranteed to be unique.
+ *
+ * - MS Docs suggest to that volume number with the file index could be used to
+ *   check if two handles refer to the same file.
+ */
+#ifndef _WIN32
+typedef struct stat                file_info_t;
+#else
+typedef BY_HANDLE_FILE_INFORMATION file_info_t;
+#endif
+
+int get_file_info(const char *fname, file_info_t *out_info)
+{
+#ifndef _WIN32
+    return stat(fname, out_info);
+#else
+    int rv = 1;
+    HANDLE h = CreateFile(fname, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
+                          FILE_ATTRIBUTE_NORMAL|FILE_FLAG_BACKUP_SEMANTICS, NULL);
+
+    if (h != INVALID_HANDLE_VALUE) {
+        rv = !GetFileInformationByHandle(h, out_info);
+        CloseHandle(h);
+    }
+    return rv;
+#endif
+}
+
+int is_dir(file_info_t *info)
+{
+#ifndef _WIN32
+    return S_ISDIR(info->st_mode);
+#else
+    return (info->dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) ==
+           FILE_ATTRIBUTE_DIRECTORY;
+#endif
+}
+
+int is_same_file(const file_info_t *fi1, const file_info_t *fi2)
+{
+#ifndef _WIN32
+    return fi1->st_dev == fi2->st_dev &&
+           fi1->st_ino == fi2->st_ino;
+#else
+    return fi1->dwVolumeSerialNumber == fi2->dwVolumeSerialNumber &&
+           fi1->nFileIndexHigh       == fi2->nFileIndexHigh &&
+           fi1->nFileIndexLow        == fi2->nFileIndexLow;
+#endif
+}
+
+static void
+tcc_normalize_inc_dirs_aux(file_info_t *stats, size_t *pnum, char **path)
+{
+    size_t i, num = *pnum;
+    if (get_file_info(*path, &stats[num]) || !is_dir(&stats[num]))
+        goto remove;
+    for (i = 0; i < num; i++)
+        if (is_same_file(&stats[i], &stats[num]))
+            goto remove;
+    *pnum = num + 1;
+    return;
+ remove:
+    tcc_free(*path);
+    *path = 0;
+}
+
+/* Remove non-existent and duplicate directories from include paths. */
+ST_FUNC void tcc_normalize_inc_dirs(TCCState *s)
+{
+    file_info_t *stats =
+        tcc_malloc(((size_t)s->nb_sysinclude_paths + s->nb_include_paths) *
+                   sizeof(*stats));
+    size_t i, num = 0;
+    for (i = 0; i < s->nb_sysinclude_paths; i++)
+        tcc_normalize_inc_dirs_aux(stats, &num, &s->sysinclude_paths[i]);
+    for (i = 0; i < s->nb_include_paths; i++)
+        tcc_normalize_inc_dirs_aux(stats, &num, &s->include_paths[i]);
+    tcc_free(stats);
+}
+
 LIBTCCAPI int tcc_set_output_type(TCCState *s, int output_type)
 {
     s->output_type = output_type;
@@ -1573,6 +1663,7 @@
     }
 #endif
 
+    tcc_normalize_inc_dirs(s);
     if (s->output_type == TCC_OUTPUT_PREPROCESS)
         print_defines();
 
diff -urN tinycc.old/tccpp.c tinycc/tccpp.c
--- tinycc.old/tccpp.c	2016-03-30 14:04:30.000000000 +0300
+++ tinycc/tccpp.c	2016-03-30 15:48:01.000000000 +0300
@@ -1663,6 +1663,7 @@
                 /* search in all the include paths */
                 int j = i - 2, k = j - s1->nb_include_paths;
                 path = k < 0 ? s1->include_paths[j] : s1->sysinclude_paths[k];
+                if (path == 0) continue;
                 pstrcpy(buf1, sizeof(buf1), path);
                 pstrcat(buf1, sizeof(buf1), "/");
             }