diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index f7409ff..b5cca28 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -6048,6 +6048,8 @@
 
 #define WUFFS_JSON__DECODER_SRC_IO_BUFFER_LENGTH_MIN_INCL 100
 
+#define WUFFS_JSON__QUIRK_ALLOW_ASCII_CONTROL_CODES 1225364480
+
 #define WUFFS_JSON__QUIRK_ALLOW_BACKSLASH_A 1225364481
 
 #define WUFFS_JSON__QUIRK_ALLOW_BACKSLASH_CAPITAL_U 1225364482
@@ -6151,6 +6153,7 @@
     wuffs_base__vtable null_vtable;
 
     bool f_quirk_enabled_allow_backslash_etc[8];
+    bool f_quirk_enabled_allow_ascii_control_codes;
     bool f_quirk_enabled_allow_backslash_capital_u;
     bool f_quirk_enabled_allow_backslash_x;
     bool f_quirk_enabled_allow_comment_block;
@@ -20842,9 +20845,9 @@
 static const uint8_t            //
     wuffs_json__lut_chars[256]  //
     WUFFS_BASE__POTENTIALLY_UNUSED = {
-        128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
-        128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
-        128, 128, 128, 128, 0,   0,   1,   0,   0,   0,   0,   0,   0,   0,
+        128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141,
+        142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155,
+        156, 157, 158, 159, 0,   0,   1,   0,   0,   0,   0,   0,   0,   0,
         0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
         0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
         0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
@@ -20855,12 +20858,12 @@
         16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,
         16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,
         16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  16,
-        16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  129, 129, 3,   3,
+        16,  16,  16,  16,  16,  16,  16,  16,  16,  16,  32,  32,  3,   3,
         3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,
         3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,   3,
         4,   4,   4,   4,   4,   4,   4,   4,   4,   4,   4,   4,   4,   4,
-        4,   4,   5,   5,   5,   5,   5,   129, 129, 129, 129, 129, 129, 129,
-        129, 129, 129, 129,
+        4,   4,   5,   5,   5,   5,   5,   32,  32,  32,  32,  32,  32,  32,
+        32,  32,  32,  32,
 };
 
 static const uint8_t              //
@@ -21041,7 +21044,9 @@
     return wuffs_base__make_empty_struct();
   }
 
-  if (a_quirk == 1225364481) {
+  if (a_quirk == 1225364480) {
+    self->private_impl.f_quirk_enabled_allow_ascii_control_codes = a_enabled;
+  } else if (a_quirk == 1225364481) {
     self->private_impl.f_quirk_enabled_allow_backslash_etc[1] = a_enabled;
   } else if (a_quirk == 1225364482) {
     self->private_impl.f_quirk_enabled_allow_backslash_capital_u = a_enabled;
@@ -21862,7 +21867,17 @@
                   goto label__string_loop_outer__continue;
                 }
               }
-              if (v_char == 128) {
+              if ((v_char & 128) != 0) {
+                if (self->private_impl
+                        .f_quirk_enabled_allow_ascii_control_codes) {
+                  *iop_a_dst++ = wuffs_base__make_token(
+                      (((uint64_t)((6291456 | ((uint32_t)((v_char & 127))))))
+                       << WUFFS_BASE__TOKEN__VALUE_MINOR__SHIFT) |
+                      (((uint64_t)(3)) << WUFFS_BASE__TOKEN__LINK__SHIFT) |
+                      (((uint64_t)(1)) << WUFFS_BASE__TOKEN__LENGTH__SHIFT));
+                  (iop_a_src += 1, wuffs_base__make_empty_struct());
+                  goto label__string_loop_outer__continue;
+                }
                 status = wuffs_base__make_status(
                     wuffs_json__error__bad_c0_control_code);
                 goto exit;
diff --git a/std/json/common_consts.wuffs b/std/json/common_consts.wuffs
index 1beeae9..18a3139 100644
--- a/std/json/common_consts.wuffs
+++ b/std/json/common_consts.wuffs
@@ -134,8 +134,8 @@
 //  - 0x04 is the start of 3-byte UTF-8.
 //  - 0x05 is the start of 4-byte UTF-8.
 //  - 0x10 is a UTF-8 tail byte.
-//  - 0x80 is invalid JSON (C0 control codes).
-//  - 0x81 is invalid UTF-8.
+//  - 0x20 is invalid UTF-8.
+//  - 0x80 and above is invalid JSON (C0 control codes).
 //
 // RFC 3629 (UTF-8) gives this grammar for valid UTF-8:
 //    UTF8-1      = %x00-7F
@@ -148,10 +148,10 @@
 pri const lut_chars array[256] base.u8 = [
 	// 0     1     2     3     4     5     6     7
 	// 8     9     A     B     C     D     E     F
-	0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,  // 0x00 ..= 0x07. C0 control codes.
-	0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,  // 0x08 ..= 0x0F. C0 control codes.
-	0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,  // 0x10 ..= 0x17. C0 control codes.
-	0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,  // 0x18 ..= 0x1F. C0 control codes.
+	0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,  // 0x00 ..= 0x07. C0 control codes.
+	0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F,  // 0x08 ..= 0x0F. C0 control codes.
+	0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,  // 0x10 ..= 0x17. C0 control codes.
+	0x98, 0x99, 0x9A, 0x9B, 0x9C, 0x9D, 0x9E, 0x9F,  // 0x18 ..= 0x1F. C0 control codes.
 	0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x20 ..= 0x27. UTF-8-1; '"'.
 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x28 ..= 0x2F. UTF-8-1.
 	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x30 ..= 0x37. UTF-8-1.
@@ -175,14 +175,14 @@
 	0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10,  // 0xB0 ..= 0xB7. UTF-8 tail.
 	0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10,  // 0xB8 ..= 0xBF. UTF-8 tail.
 
-	0x81, 0x81, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,  // 0xC0 ..= 0xC7. Invalid UTF-8; UTF-8-2.
+	0x20, 0x20, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,  // 0xC0 ..= 0xC7. Invalid UTF-8; UTF-8-2.
 	0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,  // 0xC8 ..= 0xCF. UTF-8-2.
 	0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,  // 0xD0 ..= 0xD7. UTF-8-2.
 	0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,  // 0xD8 ..= 0xDF. UTF-8-2.
 	0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04,  // 0xE0 ..= 0xE7. UTF-8-3.
 	0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04,  // 0xE8 ..= 0xEF. UTF-8-3.
-	0x05, 0x05, 0x05, 0x05, 0x05, 0x81, 0x81, 0x81,  // 0xF0 ..= 0xF7. UTF-8-4; Invalid UTF-8.
-	0x81, 0x81, 0x81, 0x81, 0x81, 0x81, 0x81, 0x81,  // 0xF8 ..= 0xFF. Invalid UTF-8.
+	0x05, 0x05, 0x05, 0x05, 0x05, 0x20, 0x20, 0x20,  // 0xF0 ..= 0xF7. UTF-8-4; Invalid UTF-8.
+	0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,  // 0xF8 ..= 0xFF. Invalid UTF-8.
 	// 0     1     2     3     4     5     6     7
 	// 8     9     A     B     C     D     E     F
 ]
diff --git a/std/json/decode_json.wuffs b/std/json/decode_json.wuffs
index eda8234..c5169d3 100644
--- a/std/json/decode_json.wuffs
+++ b/std/json/decode_json.wuffs
@@ -17,6 +17,7 @@
 	// same enum as lut_quirky_backslashes.
 	quirk_enabled_allow_backslash_etc : array[8] base.bool,
 
+	quirk_enabled_allow_ascii_control_codes             : base.bool,
 	quirk_enabled_allow_backslash_capital_u             : base.bool,
 	quirk_enabled_allow_backslash_x                     : base.bool,
 	quirk_enabled_allow_comment_block                   : base.bool,
@@ -67,7 +68,9 @@
 )
 
 pub func decoder.set_quirk_enabled!(quirk: base.u32, enabled: base.bool) {
-	if args.quirk == quirk_allow_backslash_a {
+	if args.quirk == quirk_allow_ascii_control_codes {
+		this.quirk_enabled_allow_ascii_control_codes = args.enabled
+	} else if args.quirk == quirk_allow_backslash_a {
 		this.quirk_enabled_allow_backslash_etc[1] = args.enabled
 	} else if args.quirk == quirk_allow_backslash_capital_u {
 		this.quirk_enabled_allow_backslash_capital_u = args.enabled
@@ -788,7 +791,16 @@
 							continue.string_loop_outer
 						}
 					}
-					if char == 0x80 {
+					if (char & 0x80) <> 0 {
+						if this.quirk_enabled_allow_ascii_control_codes {
+							args.dst.write_simple_token_fast!(
+								value_major: 0,
+								value_minor: 0x60_0000 | ((char & 0x7F) as base.u32),
+								link: 0x3,
+								length: 1)
+							args.src.skip32_fast!(actual: 1, worst_case: 1)
+							continue.string_loop_outer
+						}
 						return "#bad C0 control code"
 					}
 					if this.quirk_enabled_replace_invalid_unicode {
diff --git a/std/json/decode_quirks.wuffs b/std/json/decode_quirks.wuffs
index fdb14b2..7feb5af 100644
--- a/std/json/decode_quirks.wuffs
+++ b/std/json/decode_quirks.wuffs
@@ -21,6 +21,20 @@
 
 // --------
 
+// When this quirk is enabled, literal (not escaped) ASCII control codes, such
+// as backspaces, new lines and NUL bytes, are accepted in JSON strings.
+//
+// Regardless of whether this quirk is enabled, escaped ASCII control codes,
+// such as "\b" or "\u0008", are always accepted.
+//
+// This allows for multi-line strings, where a literal new line in the encoding
+// becomes a literal new line in the decoding. A backslash before a new line is
+// still a syntax error, unless combined with quirk_allow_backslash_new_line.
+//
+// Any indentation following a new line is not stripped, but remains part of
+// the decoded string.
+pub const quirk_allow_ascii_control_codes base.u32 = 0x4909_9400 | 0x00
+
 // When this quirk is enabled, e.g. "abc\az" is accepted as a JSON string,
 // equivalent to "abc\u0007z", containing an ASCII Bell control character.
 pub const quirk_allow_backslash_a base.u32 = 0x4909_9400 | 0x01
diff --git a/test/c/std/json.c b/test/c/std/json.c
index 8ea6bc5..42f259e 100644
--- a/test/c/std/json.c
+++ b/test/c/std/json.c
@@ -1414,6 +1414,11 @@
     uint32_t quirk;
   } test_cases[] = {
       {
+          .want = 0x09,
+          .str = "\"\t\"",
+          .quirk = WUFFS_JSON__QUIRK_ALLOW_ASCII_CONTROL_CODES,
+      },
+      {
           .want = 0x07,
           .str = "\"\\a\"",
           .quirk = WUFFS_JSON__QUIRK_ALLOW_BACKSLASH_A,
@@ -1475,6 +1480,11 @@
               .repr;
       const char* want_status_repr =
           q ? NULL : wuffs_json__error__bad_backslash_escape;
+      if ((test_cases[tc].quirk ==
+           WUFFS_JSON__QUIRK_ALLOW_ASCII_CONTROL_CODES) &&
+          want_status_repr) {
+        want_status_repr = wuffs_json__error__bad_c0_control_code;
+      }
       if (have_status_repr != want_status_repr) {
         RETURN_FAIL("tc=%d, q=%d: decode_tokens: have \"%s\", want \"%s\"", tc,
                     q, have_status_repr, want_status_repr);