diff --git a/include/ft/all-tests.h b/include/ft/all-tests.h
index 84e29f6..1fd8ebd 100644
--- a/include/ft/all-tests.h
+++ b/include/ft/all-tests.h
@@ -31,6 +31,8 @@ extern ft_test ft_stdio_open;
 extern ft_test ft_stdio_simple_read;
 extern ft_test ft_stdio_simple_write;
 extern ft_test ft_stdio_line_buffering;
+extern ft_test ft_stdio_update_ungetc;
+extern ft_test ft_stdio_append;
 
 /* stdlib */
 extern ft_test ft_stdlib_arith;
diff --git a/src/main.c b/src/main.c
index 2b2524a..13eba97 100644
--- a/src/main.c
+++ b/src/main.c
@@ -47,6 +47,8 @@ ft_list headers_libc[] = {
         &ft_stdio_simple_read,
         &ft_stdio_simple_write,
         &ft_stdio_line_buffering,
+        &ft_stdio_update_ungetc,
+        &ft_stdio_append,
         NULL,
     }},
     { _("stdlib.h", "<stdlib.h>"), (ft_test*[]){
diff --git a/src/stdio/files.c b/src/stdio/files.c
index b9d912a..a72be32 100644
--- a/src/stdio/files.c
+++ b/src/stdio/files.c
@@ -29,8 +29,8 @@ static void _stdio_open_switch(ft_test *t)
 	/* Try to open it with <stdio.h> */
 	DO_E(fp, fopen("ft_stdio.txt", "r"), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
-	if(!fp) return;
 
 	/* Change buffer settings a couple times */
 	DO_E(rc, setvbuf(fp, NULL, _IONBF, 0), t, "%d");
@@ -46,15 +46,19 @@ static void _stdio_open_switch(ft_test *t)
 	/* Reopen with different permissions */
 	DO_E(fp, freopen("ft_stdio.txt", "w+", fp), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 	DO_E(fp, freopen("ft_stdio.txt", "rb+", fp), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 	DO_E(fp, freopen("ft_stdio.txt", "ab", fp), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 	DO_E(fp, freopen("ft_stdio.txt", "w", fp), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 
 	DO_E(rc, fclose(fp), t, "%d");
@@ -80,7 +84,7 @@ static char const *filler =
 "defined) is advanced by the number of characters successfully read. If an "
 "error occurs, the resulting value of the file position indicator for the "
 "stream is indeterminate. If a partial element is read, its value is "
-"indeterminate.\n"; /* length 591 */
+"indeterminate.\n"; /* ISO/IEC 9899:1999, 7.19.8.1§2 (length 591) */
 
 static void _ft_stdio_simple_read_switch(ft_test *t)
 {
@@ -100,6 +104,7 @@ static void _ft_stdio_simple_read_switch(ft_test *t)
 	/* Read it through a buffer of size 128 */
 	DO_E(fp, fopen("ft_stdio.txt", "r"), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 	DO_E(rc, setvbuf(fp, NULL, _IOFBF, 128), t, "%d");
 	ft_assert(t, rc == 0);
@@ -264,6 +269,7 @@ static void _ft_stdio_simple_write_switch(ft_test *t)
 	/* Open a new file */
 	DO_E(fp, fopen("ft_stdio.txt", "w"), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 	DO_E(rc, setvbuf(fp, NULL, _IOFBF, 128), t, "%d");
 	ft_assert(t, rc == 0);
@@ -347,6 +353,7 @@ static void _ft_stdio_simple_write_switch(ft_test *t)
 	/* Check the new file size */
 	DO_E(fp, fopen("ft_stdio.txt", "r"), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	DO_E(rc, fseek(fp, 0, SEEK_END), t, "%d");
 	ft_assert(t, rc == 0);
 	DO_E(rc, ftell(fp), t, "%d");
@@ -373,6 +380,7 @@ static void _ft_stdio_line_buffering_switch(ft_test *t)
 	/* Open a new line-buffered file */
 	DO_E(fp, fopen("ft_stdio.txt", "w"), t, "%p");
 	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
 	ft_log_FILE(t, "", fp);
 	DO_E(rc, setvbuf(fp, NULL, _IOLBF, 128), t, "%d");
 	ft_assert(t, rc == 0);
@@ -424,3 +432,241 @@ ft_test ft_stdio_line_buffering = {
 	.name = "Writing with line buffering",
 	.function = _ft_stdio_line_buffering,
 };
+
+static void _ft_stdio_update_ungetc_switch(ft_test *t)
+{
+	FILE *fp;
+	int rc;
+	char str[128];
+
+	/* Create a file in update mode with w+ */
+	DO_E(fp, fopen("ft_stdio.txt", "w+"), t, "%p");
+	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
+	ft_log_FILE(t, "", fp);
+	/* Write some data, then re-read it, then re-write it */
+	DO_E(rc, fwrite(filler, 1, 64, fp), t, "%d");
+	ft_assert(t, rc == 64);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fseek(fp, 0, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fread(str, 1, 16, fp), t, "%d");
+	ft_assert(t, rc == 16);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fread(str, 1, 48, fp), t, "%d");
+	ft_assert(t, rc == 48);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, ftell(fp) == 64);
+	DO_E(rc, fseek(fp, -16, SEEK_CUR), t, "%d");
+	ft_assert(t, rc == 0);
+	DO_E(rc, fwrite(str, 1, 48, fp), t, "%d");
+	ft_assert(t, rc == 48);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fwrite(str, 1, 16, fp), t, "%d");
+	ft_assert(t, rc == 16);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, ftell(fp) == 112);
+	/* Re-read it and check it */
+	rewind(fp);
+	ft_log(t, "rewind(fp)\n");
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fread(str, 1, 112, fp), t, "%d");
+	ft_assert(t, rc == 112);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, !memcmp(str, filler, 48));
+	ft_assert(t, !memcmp(str+48, filler+16, 48));
+	ft_assert(t, !memcmp(str+96, filler+16, 16));
+	DO_E(rc, fclose(fp), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_log(t, "\n");
+
+	/* Reopen that file with r+ */
+	DO_E(fp, fopen("ft_stdio.txt", "r+"), t, "%p");
+	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
+	ft_log_FILE(t, "", fp);
+	/* ungetc() some characters before position 0 */
+	DO_E(rc, ungetc('#', fp), t, "'%c'");
+	ft_assert(t, rc == '#');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('!', fp), t, "'%c'");
+	ft_assert(t, rc == '!');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('$', fp), t, "'%c'");
+	ft_assert(t, rc == '$');
+	ft_log_FILE(t, "", fp);
+	/* Read them back along with some actual data */
+	DO_E(rc, fread(str, 1, 51, fp), t, "%d");
+	ft_assert(t, rc == 51);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, !memcmp(str, "$!#", 3) && !memcmp(str+3, filler, 48));
+	/* Do it again after position 0 */
+	DO_E(rc, ungetc('#', fp), t, "'%c'");
+	ft_assert(t, rc == '#');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('!', fp), t, "'%c'");
+	ft_assert(t, rc == '!');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('$', fp), t, "'%c'");
+	ft_assert(t, rc == '$');
+	ft_log_FILE(t, "", fp);
+	/* Read them back as well as the second segment */
+	DO_E(rc, fread(str, 1, 51, fp), t, "%d");
+	ft_assert(t, rc == 51);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, !memcmp(str, "$!#", 3) && !memcmp(str+3, filler+16, 48));
+	/* Push some characters but discard them by rewind() */
+	DO_E(rc, ungetc('#', fp), t, "'%c'");
+	ft_assert(t, rc == '#');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fseek(fp, 0, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fread(str, 1, 48, fp), t, "%d");
+	ft_assert(t, rc == 48);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, !memcmp(str, filler, 48));
+	/* Discard buffered data by a write (nonstandard but supported) */
+	DO_E(rc, fwrite(filler, 1, 48, fp), t, "%d");
+	ft_assert(t, rc == 48);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fclose(fp), t, "%d");
+	ft_assert(t, rc == 0);
+
+	/* Try ungetc() like previousy but with a non-buffered stream */
+	DO_E(fp, fopen("ft_stdio.txt", "r+"), t, "%p");
+	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, setvbuf(fp, NULL, _IONBF, 0), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fseek(fp, 0, SEEK_END), t, "%d");
+	ft_assert(t, rc == 0);
+	DO_E(rc, ftell(fp), t, "%d");
+	ft_assert(t, rc == 112);
+	DO_E(rc, fseek(fp, 0, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	/* ungetc() some characters before position 0 */
+	DO_E(rc, ungetc('#', fp), t, "'%c'");
+	ft_assert(t, rc == '#');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('!', fp), t, "'%c'");
+	ft_assert(t, rc == '!');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('$', fp), t, "'%c'");
+	ft_assert(t, rc == '$');
+	ft_log_FILE(t, "", fp);
+	/* Read them back along with some actual data */
+	DO_E(rc, fread(str, 1, 51, fp), t, "%d");
+	ft_assert(t, rc == 51);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, !memcmp(str, "$!#", 3) && !memcmp(str+3, filler, 48));
+	/* Do it again after position 0 */
+	DO_E(rc, ungetc('#', fp), t, "'%c'");
+	ft_assert(t, rc == '#');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('!', fp), t, "'%c'");
+	ft_assert(t, rc == '!');
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ungetc('$', fp), t, "'%c'");
+	ft_assert(t, rc == '$');
+	ft_log_FILE(t, "", fp);
+	/* Read them back as well as the second segment */
+	DO_E(rc, fread(str, 1, 51, fp), t, "%d");
+	ft_assert(t, rc == 51);
+	ft_log_FILE(t, "", fp);
+	ft_assert(t, !memcmp(str, "$!#", 3) && !memcmp(str+3, filler, 48));
+	DO_E(rc, fclose(fp), t, "%d");
+	ft_assert(t, rc == 0);
+}
+
+static void _ft_stdio_update_ungetc(ft_test *t)
+{
+	gint_world_switch(GINT_CALL(_ft_stdio_update_ungetc_switch,
+		(void *)t));
+}
+
+ft_test ft_stdio_update_ungetc = {
+	.name = "Update modes and ungetc()",
+	.function = _ft_stdio_update_ungetc,
+};
+
+static void _ft_stdio_append_switch(ft_test *t)
+{
+	FILE *fp;
+	int rc;
+	char str[40];
+
+	/* Remove the file if it exists */
+	DO_E(rc, remove("ft_append.txt"), t, "%d");
+	ft_assert(t, rc == 0 || (rc == -1 && errno == ENOENT));
+
+	/* Append some data with mode a */
+	DO_E(fp, fopen("ft_append.txt", "a"), t, "%p");
+	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fwrite("Line #1\n", 1, 8, fp), t, "%d");
+	ft_assert(t, rc == 8);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fseek(fp, 0, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_assert(t, ftell(fp) == 0);
+	DO_E(rc, fwrite("Line #2\n", 1, 8, fp), t, "%d");
+	ft_assert(t, rc == 8);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ftell(fp), t, "%d");
+	ft_assert(t, rc == 16);
+	DO_E(rc, fclose(fp), t, "%d");
+	ft_assert(t, rc == 0);
+
+	/* Append more with a+ */
+	DO_E(fp, fopen("ft_append.txt", "a+"), t, "%p");
+	ft_assert(t, fp != NULL);
+	if(fp == NULL) return;
+	DO_E(rc, fseek(fp, 0, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_assert(t, ftell(fp) == 0);
+	DO_E(rc, fread(str, 1, 8, fp), t, "%d");
+	ft_assert(t, rc == 8);
+	ft_assert(t, ftell(fp) == 8);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fwrite(str, 1, 8, fp), t, "%d");
+	ft_assert(t, rc == 8);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ftell(fp), t, "%d");
+	ft_assert(t, rc == 24);
+	DO_E(rc, fseek(fp, 8, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	DO_E(rc, fread(str, 1, 16, fp), t, "%d");
+	ft_assert(t, rc == 16);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, fseek(fp, -8, SEEK_END), t, "%d");
+	ft_assert(t, rc == 0);
+	ft_assert(t, ftell(fp) == 16);
+	DO_E(rc, fwrite(str, 1, 16, fp), t, "%d");
+	ft_assert(t, rc == 16);
+	ft_log_FILE(t, "", fp);
+	DO_E(rc, ftell(fp), t, "%d");
+	ft_assert(t, rc == 40);
+	DO_E(rc, fseek(fp, 0, SEEK_SET), t, "%d");
+	ft_assert(t, rc == 0);
+	DO_E(rc, fread(str, 1, 40, fp), t, "%d");
+	ft_assert(t, rc == 40);
+	ft_assert(t, !memcmp(str,
+		"Line #1\nLine #2\nLine #1\nLine #2\nLine #1\n", 40));
+	DO_E(rc, fclose(fp), t, "%d");
+	ft_assert(t, rc == 0);
+}
+
+static void _ft_stdio_append(ft_test *t)
+{
+	gint_world_switch(GINT_CALL(_ft_stdio_append_switch, (void *)t));
+}
+
+ft_test ft_stdio_append = {
+	.name = "Append modes",
+	.function = _ft_stdio_append,
+};
diff --git a/src/stdio/util.h b/src/stdio/util.h
index b60e02e..89a9494 100644
--- a/src/stdio/util.h
+++ b/src/stdio/util.h
@@ -25,8 +25,8 @@ static inline void ft_log_FILE(ft_test *t, char const *prefix, FILE *fp)
         fp->bufmode == _IOLBF ? "_IOLBF" :
         fp->bufmode == _IOFBF ? "_IOFBF" : "_???");
 
-    if(fp->bufmode != _IONBF) {
-        ft_log(t, " %p/%d", fp->buf, fp->bufsize);
+    if(fp->buf) {
+        ft_log(t, " %s%d", fp->buf ? "" : "NULL/", fp->bufsize);
 
         if(fp->bufpos == 0)
             ft_log(t, " EMPTY");
@@ -34,6 +34,9 @@ static inline void ft_log_FILE(ft_test *t, char const *prefix, FILE *fp)
             ft_log(t, " READ %d/%d", fp->bufpos, fp->bufread);
         else if(fp->bufdir == __FILE_BUF_WRITE)
             ft_log(t, " WRITE %d", fp->bufpos);
+
+        if(fp->bufungetc > 0)
+            ft_log(t, " UNGETC %d", fp->bufungetc);
     }
 
     ft_log(t, "}\n");