diff --git a/lib/std/collections/anylist.c3 b/lib/std/collections/anylist.c3
index 30fb898fd..7ca04eb39 100644
--- a/lib/std/collections/anylist.c3
+++ b/lib/std/collections/anylist.c3
@@ -96,7 +96,7 @@ fn void AnyList.free_element(&self, any element) @inline
  Pop a value who's type is known. If the type is incorrect, this
  will still pop the element.
 
- @return! TYPE_MISMATCH, NO_MORE_ELEMENT
+ @return? TYPE_MISMATCH, NO_MORE_ELEMENT
 *>
 macro AnyList.pop(&self, $Type)
 {
@@ -107,7 +107,7 @@ macro AnyList.pop(&self, $Type)
 
 <*
  Pop the last value and allocate the copy using the given allocator.
- @return! NO_MORE_ELEMENT
+ @return? NO_MORE_ELEMENT
 *>
 fn any? AnyList.copy_pop(&self, Allocator allocator)
 {
@@ -119,13 +119,13 @@ fn any? AnyList.copy_pop(&self, Allocator allocator)
 
 <*
  Pop the last value and allocate the copy using the temp allocator
- @return! NO_MORE_ELEMENT
+ @return? NO_MORE_ELEMENT
 *>
 fn any? AnyList.tcopy_pop(&self) => self.copy_pop(tmem());
 
 <*
  Pop the last value. It must later be released using list.free_element()
- @return! NO_MORE_ELEMENT
+ @return? NO_MORE_ELEMENT
 *>
 fn any? AnyList.pop_retained(&self)
 {
diff --git a/lib/std/compression/qoi.c3 b/lib/std/compression/qoi.c3
index 00b55e658..02cba0ec7 100644
--- a/lib/std/compression/qoi.c3
+++ b/lib/std/compression/qoi.c3
@@ -94,7 +94,7 @@ fn usz? write(String filename, char[] input, QOIDesc* desc) => @pool()
  @param [in] filename : `The file's name to read the image from`
  @param [&out] desc : `The descriptor to fill with the image's info`
  @param channels : `The channels to be used`
- @return! FILE_OPEN_FAILED, INVALID_DATA, TOO_MANY_PIXELS
+ @return? FILE_OPEN_FAILED, INVALID_DATA, TOO_MANY_PIXELS
 *>
 fn char[]? read(Allocator allocator, String filename, QOIDesc* desc, QOIChannels channels = AUTO) => @pool(allocator)
 {
@@ -122,7 +122,7 @@ import std::bits;
 
  @param [in] input : `The raw RGB or RGBA pixels to encode`
  @param [&in] desc : `The descriptor of the image`
- @return! INVALID_PARAMETERS, TOO_MANY_PIXELS, INVALID_DATA
+ @return? INVALID_PARAMETERS, TOO_MANY_PIXELS, INVALID_DATA
 *>
 fn char[]? encode(Allocator allocator, char[] input, QOIDesc* desc) @nodiscard
 {
@@ -277,7 +277,7 @@ fn char[]? encode(Allocator allocator, char[] input, QOIDesc* desc) @nodiscard
  @param [in] data : `The QOI image data to decode`
  @param [&out] desc : `The descriptor to fill with the image's info`
  @param channels : `The channels to be used`
- @return! INVALID_DATA, TOO_MANY_PIXELS
+ @return? INVALID_DATA, TOO_MANY_PIXELS
 *>
 fn char[]? decode(Allocator allocator, char[] data, QOIDesc* desc, QOIChannels channels = AUTO) @nodiscard
 {
@@ -406,7 +406,7 @@ const char[*] END_OF_STREAM = {0, 0, 0, 0, 0, 0, 0, 1};
 // inefficient, but it's only run once at a time
 
 <*
- @return! INVALID_DATA
+ @return? INVALID_DATA
 *>
 macro @enumcast($Type, raw)
 {
diff --git a/lib/std/core/allocators/arena_allocator.c3 b/lib/std/core/allocators/arena_allocator.c3
index 32a748984..672477dc6 100644
--- a/lib/std/core/allocators/arena_allocator.c3
+++ b/lib/std/core/allocators/arena_allocator.c3
@@ -57,7 +57,7 @@ fn void ArenaAllocator.reset(&self, usz mark) @dynamic => self.used = mark;
  @require !alignment || math::is_power_of_2(alignment)
  @require alignment <= mem::MAX_MEMORY_ALIGNMENT : `alignment too big`
  @require size > 0
- @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+ @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 *>
 fn void*? ArenaAllocator.acquire(&self, usz size, AllocInitType init_type, usz alignment) @dynamic
 {
@@ -81,7 +81,7 @@ fn void*? ArenaAllocator.acquire(&self, usz size, AllocInitType init_type, usz a
  @require alignment <= mem::MAX_MEMORY_ALIGNMENT : `alignment too big`
  @require old_pointer != null
  @require size > 0
- @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+ @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 *>
 fn void*? ArenaAllocator.resize(&self, void *old_pointer, usz size, usz alignment) @dynamic
 {
diff --git a/lib/std/core/allocators/dynamic_arena.c3 b/lib/std/core/allocators/dynamic_arena.c3
index 86963ab9b..5fd3ec751 100644
--- a/lib/std/core/allocators/dynamic_arena.c3
+++ b/lib/std/core/allocators/dynamic_arena.c3
@@ -78,7 +78,7 @@ fn void DynamicArenaAllocator.release(&self, void* ptr, bool) @dynamic
  @require size > 0 : `Resize doesn't support zeroing`
  @require old_pointer != null : `Resize doesn't handle null pointers`
  @require self.page != null  : `tried to realloc pointer on invalid allocator`
- @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+ @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 *>
 fn void*? DynamicArenaAllocator.resize(&self, void* old_pointer, usz size, usz alignment) @dynamic
 {
@@ -130,7 +130,7 @@ fn void DynamicArenaAllocator.reset(&self, usz mark = 0) @dynamic
 <*
  @require math::is_power_of_2(alignment)
  @require size > 0
- @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+ @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 *>
 fn void*? DynamicArenaAllocator._alloc_new(&self, usz size, usz alignment) @local
 {
@@ -161,7 +161,7 @@ fn void*? DynamicArenaAllocator._alloc_new(&self, usz size, usz alignment) @loca
 <*
  @require size > 0 : `acquire expects size > 0`
  @require !alignment || math::is_power_of_2(alignment)
- @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+ @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 *>
 fn void*? DynamicArenaAllocator.acquire(&self, usz size, AllocInitType init_type, usz alignment) @dynamic
 {
diff --git a/lib/std/core/array.c3 b/lib/std/core/array.c3
index ca0bce992..3c440266a 100644
--- a/lib/std/core/array.c3
+++ b/lib/std/core/array.c3
@@ -5,7 +5,7 @@ import std::core::array::slice;
  @param [in] array
  @param [in] element
  @return "the first index of the element"
- @return! NOT_FOUND
+ @return? NOT_FOUND
 *>
 macro index_of(array, element)
 {
@@ -34,7 +34,7 @@ macro slice2d(array_ptr, x = 0, xlen = 0, y = 0, ylen = 0)
  @param [in] array
  @param [in] element
  @return "the last index of the element"
- @return! NOT_FOUND
+ @return? NOT_FOUND
 *>
 macro rindex_of(array, element)
 {
diff --git a/lib/std/core/builtin.c3 b/lib/std/core/builtin.c3
index 97fb66d7a..b550b9bb3 100644
--- a/lib/std/core/builtin.c3
+++ b/lib/std/core/builtin.c3
@@ -79,7 +79,7 @@ macro void @swap(#a, #b) @builtin
  @param $Type : `the type to convert to`
  @return `The any.ptr converted to its type.`
  @ensure @typeis(return, $Type*)
- @return! TYPE_MISMATCH
+ @return? TYPE_MISMATCH
 *>
 macro anycast(any v, $Type) @builtin
 {
@@ -247,7 +247,7 @@ macro bitcast(expr, $Type) @builtin
  @param [in] enum_name : `The name of the enum to search for`
  @require $Type.kindof == ENUM : `Only enums may be used`
  @ensure @typeis(return, $Type)
- @return! NOT_FOUND
+ @return? NOT_FOUND
 *>
 macro enum_by_name($Type, String enum_name) @builtin
 {
@@ -265,7 +265,7 @@ macro enum_by_name($Type, String enum_name) @builtin
  @require $defined($Type.#value) : `Expected '#value' to match an enum associated value`
  @require $assignable(value, $typeof(($Type){}.#value)) : `Expected the value to match the type of the associated value`
  @ensure @typeis(return, $Type)
- @return! NOT_FOUND
+ @return? NOT_FOUND
 *>
 macro @enum_from_value($Type, #value, value) @builtin
 {
diff --git a/lib/std/core/conv.c3 b/lib/std/core/conv.c3
index 83aa304ea..7ffbadf62 100644
--- a/lib/std/core/conv.c3
+++ b/lib/std/core/conv.c3
@@ -12,7 +12,7 @@ const uint UTF16_SURROGATE_HIGH_VALUE @private = 0xD800;
 <*
  @param c : `The utf32 codepoint to convert`
  @param [out] output : `the resulting buffer`
- @return! string::CONVERSION_FAILED
+ @return? string::CONVERSION_FAILED
 *>
 fn usz? char32_to_utf8(Char32 c, char[] output)
 {
diff --git a/lib/std/core/mem_allocator.c3 b/lib/std/core/mem_allocator.c3
index 4304f81e0..7279e95bd 100644
--- a/lib/std/core/mem_allocator.c3
+++ b/lib/std/core/mem_allocator.c3
@@ -24,7 +24,7 @@ interface Allocator
 	 @require !alignment || math::is_power_of_2(alignment)
 	 @require alignment <= mem::MAX_MEMORY_ALIGNMENT : `alignment too big`
 	 @require size > 0
-	 @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+	 @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 	*>
 	fn void*? acquire(usz size, AllocInitType init_type, usz alignment = 0);
 	<*
@@ -32,7 +32,7 @@ interface Allocator
 	 @require alignment <= mem::MAX_MEMORY_ALIGNMENT : `alignment too big`
 	 @require ptr != null
 	 @require new_size > 0
-	 @return! mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
+	 @return? mem::INVALID_ALLOC_SIZE, mem::OUT_OF_MEMORY
 	*>
 	fn void*? resize(void* ptr, usz new_size, usz alignment = 0);
 	<*
diff --git a/lib/std/core/string.c3 b/lib/std/core/string.c3
index 1dd2a8ed9..302daaadf 100644
--- a/lib/std/core/string.c3
+++ b/lib/std/core/string.c3
@@ -290,7 +290,7 @@ fault BUFFER_EXCEEDED;
  @param max : "Max number of elements, 0 means no limit, defaults to 0"
  @require needle.len > 0 : "The needle must be at least 1 character long"
  @ensure return.len > 0
- @return! BUFFER_EXCEEDED : `If there are more elements than would fit the buffer`
+ @return? BUFFER_EXCEEDED : `If there are more elements than would fit the buffer`
 *>
 fn String[]? String.split_to_buffer(s, String needle, String[] buffer, usz max = 0, bool skip_empty = false)
 {
@@ -345,7 +345,7 @@ fn bool String.contains(s, String needle)
  @pure
  @ensure return < s.len
  @return "the index of the needle"
- @return! NOT_FOUND : "if the needle cannot be found"
+ @return? NOT_FOUND : "if the needle cannot be found"
 *>
 fn usz? String.index_of_char(s, char needle)
 {
@@ -364,7 +364,7 @@ fn usz? String.index_of_char(s, char needle)
  @pure
  @ensure return < s.len
  @return "the index of the needle"
- @return! NOT_FOUND : "if the needle cannot be found"
+ @return? NOT_FOUND : "if the needle cannot be found"
 *>
 fn usz? String.index_of_chars(String s, char[] needle)
 {
@@ -388,7 +388,7 @@ fn usz? String.index_of_chars(String s, char[] needle)
  @pure
  @ensure return < s.len
  @return "the index of the needle"
- @return! NOT_FOUND : "if the needle cannot be found starting from the start_index"
+ @return? NOT_FOUND : "if the needle cannot be found starting from the start_index"
 *>
 fn usz? String.index_of_char_from(s, char needle, usz start_index)
 {
@@ -409,7 +409,7 @@ fn usz? String.index_of_char_from(s, char needle, usz start_index)
  @pure
  @ensure return < s.len
  @return "the index of the needle"
- @return! NOT_FOUND : "if the needle cannot be found"
+ @return? NOT_FOUND : "if the needle cannot be found"
 *>
 fn usz? String.rindex_of_char(s, char needle)
 {
@@ -429,7 +429,7 @@ fn usz? String.rindex_of_char(s, char needle)
  @ensure return < s.len
  @require needle.len > 0 : "The needle must be len 1 or more"
  @return "the index of the needle"
- @return! NOT_FOUND : "if the needle cannot be found"
+ @return? NOT_FOUND : "if the needle cannot be found"
 *>
 fn usz? String.index_of(s, String needle)
 {
@@ -454,7 +454,7 @@ fn usz? String.index_of(s, String needle)
  @ensure return < s.len
  @require needle.len > 0 : "The needle must be len 1 or more"
  @return "the index of the needle"
- @return! NOT_FOUND : "if the needle cannot be found"
+ @return? NOT_FOUND : "if the needle cannot be found"
 *>
 fn usz? String.rindex_of(s, String needle)
 {
@@ -556,7 +556,7 @@ fn String ZString.tcopy(z)
 <*
  Convert an UTF-8 string to UTF-16
  @return "The UTF-16 string as a slice, allocated using the given allocator"
- @return! INVALID_UTF8 : "If the string contained an invalid UTF-8 sequence"
+ @return? INVALID_UTF8 : "If the string contained an invalid UTF-8 sequence"
 *>
 fn Char16[]? String.to_utf16(s, Allocator allocator)
 {
diff --git a/lib/std/encoding/base32.c3 b/lib/std/encoding/base32.c3
index 7a9296196..912716982 100644
--- a/lib/std/encoding/base32.c3
+++ b/lib/std/encoding/base32.c3
@@ -84,7 +84,7 @@ fn usz encode_len(usz n, char padding)
  @require padding < 0xFF : "Invalid padding character"
  @require dst.len >= decode_len(src.len, padding) : "Destination buffer too small"
  @return "The resulting dst buffer"
- @return! encoding::INVALID_PADDING, encoding::INVALID_CHARACTER
+ @return? encoding::INVALID_PADDING, encoding::INVALID_CHARACTER
 *>
 fn char[]? decode_buffer(char[] src, char[] dst, char padding = DEFAULT_PAD, Base32Alphabet* alphabet = &STANDARD)
 {
diff --git a/lib/std/encoding/base64.c3 b/lib/std/encoding/base64.c3
index e5e8c64e1..4bb6ef92a 100644
--- a/lib/std/encoding/base64.c3
+++ b/lib/std/encoding/base64.c3
@@ -79,7 +79,7 @@ fn usz encode_len(usz n, char padding)
  @param padding : "The padding character or 0 if none"
  @require padding < 0xFF : "Invalid padding character"
  @return "The size of the input once decoded."
- @return! encoding::INVALID_PADDING
+ @return? encoding::INVALID_PADDING
 *>
 fn usz? decode_len(usz n, char padding)
 {
@@ -163,7 +163,7 @@ fn String encode_buffer(char[] src, char[] dst, char padding = DEFAULT_PAD, Base
  @require (decode_len(src.len, padding) ?? 0) <= dst.len : "Destination buffer too small"
  @require padding < 0xFF : "Invalid padding character"
  @return "The decoded data."
- @return! encoding::INVALID_CHARACTER, encoding::INVALID_PADDING
+ @return? encoding::INVALID_CHARACTER, encoding::INVALID_PADDING
 *>
 fn char[]? decode_buffer(char[] src, char[] dst, char padding = DEFAULT_PAD, Base64Alphabet* alphabet = &STANDARD)
 {
diff --git a/lib/std/encoding/hex.c3 b/lib/std/encoding/hex.c3
index be6b24d79..6e528ed3e 100644
--- a/lib/std/encoding/hex.c3
+++ b/lib/std/encoding/hex.c3
@@ -72,7 +72,7 @@ macro usz decode_len(usz n) => n / 2;
  @param dst : "The decoded input."
  @require src.len % 2 == 0 : "src is not of even length"
  @require dst.len >= decode_len(src.len) : "Destination array is not large enough"
- @return! encoding::INVALID_CHARACTER
+ @return? encoding::INVALID_CHARACTER
 *>
 fn usz? decode_bytes(char[] src, char[] dst)
 {
diff --git a/lib/std/io/path.c3 b/lib/std/io/path.c3
index de2d41530..e5904e82e 100644
--- a/lib/std/io/path.c3
+++ b/lib/std/io/path.c3
@@ -109,7 +109,7 @@ macro bool? mkdir(Path path, bool recursive = false, MkdirPermissions permission
  @param path : `The path to delete`
  @require @is_pathlike(path) : "Expected a Path or String to chdir"
  @return `true if there was a directory to delete, false otherwise`
- @return! INVALID_PATH : `if the path was invalid`
+ @return? INVALID_PATH : `if the path was invalid`
 *>
 macro bool? rmdir(path)
 {
@@ -136,7 +136,7 @@ fn void? rmtree(Path path)
 <*
  Creates a new path.
 
- @return! INVALID_PATH : `if the path was invalid`
+ @return? INVALID_PATH : `if the path was invalid`
 *>
 fn Path? new(Allocator allocator, String path, PathEnv path_env = DEFAULT_ENV)
 {
@@ -146,7 +146,7 @@ fn Path? new(Allocator allocator, String path, PathEnv path_env = DEFAULT_ENV)
 <*
  Creates a new path using the temp allocator.
 
- @return! INVALID_PATH : `if the path was invalid`
+ @return? INVALID_PATH : `if the path was invalid`
 *>
 fn Path? temp(String path, PathEnv path_env = DEFAULT_ENV)
 {
@@ -391,7 +391,7 @@ fn usz? volume_name_len(String path, PathEnv path_env) @local
  of the path itself.
 
  @return `The parent of the path as a non-allocated path`
- @return! NO_PARENT : `if this path does not have a parent`
+ @return? NO_PARENT : `if this path does not have a parent`
 *>
 fn Path? Path.parent(self)
 {
diff --git a/lib/std/net/url_encoding.c3 b/lib/std/net/url_encoding.c3
index 48ef50f57..fa506d6a4 100644
--- a/lib/std/net/url_encoding.c3
+++ b/lib/std/net/url_encoding.c3
@@ -105,7 +105,7 @@ fn String tencode(String s, UrlEncodingMode mode) => encode(tmem(), s, mode);
 <*
  Calculate the length of the percent-decoded string.
 
- @return! INVALID_HEX
+ @return? INVALID_HEX
 *>
 fn usz? decode_len(String s, UrlEncodingMode mode) @inline
 {
diff --git a/lib/std/os/env.c3 b/lib/std/os/env.c3
index 2726bf924..2f0cf02ba 100644
--- a/lib/std/os/env.c3
+++ b/lib/std/os/env.c3
@@ -7,7 +7,7 @@ import std::io::path, libc, std::os;
 <*
  @param [in] name
  @require name.len > 0
- @return! NOT_FOUND
+ @return? NOT_FOUND
 *>
 fn String? get_var(Allocator allocator, String name) => @pool(allocator)
 {
diff --git a/releasenotes.md b/releasenotes.md
index e14a9450a..2314fe714 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -22,7 +22,7 @@
 - `$for` "()" replaced by trailing ":" `$for (var $x = 0; $x < FOO; $x++)` -> `$for var $x = 0; $x < FOO; $x++:`
 - `$switch` "()" replaced by trailing ":" `$switch ($Type)` -> `$switch $Type:`
 - Empty `$switch` requires trailing ":" `$switch` -> `$switch:`
-- Change `@return!` syntax to require ":" after faults.
+- Rename `@return` to `@return?` and change syntax to require ":" after faults.
 - Remove `if (catch foo) { case ... }` syntax.
 - Remove `[?]` syntax.
 - Change `int!` to `int?` syntax.
diff --git a/src/compiler/parse_global.c b/src/compiler/parse_global.c
index a324c5243..c7b9f21d8 100644
--- a/src/compiler/parse_global.c
+++ b/src/compiler/parse_global.c
@@ -2770,7 +2770,7 @@ static bool parse_contracts(ParseContext *c, AstId *contracts_ref)
 		else if (name == kw_at_return)
 		{
 			advance(c);
-			if (tok_is(c, TOKEN_BANG))
+			if (tok_is(c, TOKEN_QUESTION))
 			{
 				if (!parse_doc_optreturn(c, contracts_ref, next)) return false;
 			}
diff --git a/test/test_suite/errors/optional_contracts.c3 b/test/test_suite/errors/optional_contracts.c3
index 00cef7e58..1c89ed6a3 100644
--- a/test/test_suite/errors/optional_contracts.c3
+++ b/test/test_suite/errors/optional_contracts.c3
@@ -8,7 +8,7 @@ fault XYZ;
 <*
 
  hello world
- @return! XYZ, ABC
+ @return? XYZ, ABC
  *>
 fn void? abc(int a, int b, int z)
 {
@@ -17,7 +17,7 @@ fn void? abc(int a, int b, int z)
 
 <*
 hello world
- @return! XYZ, ABC
+ @return? XYZ, ABC
  *>
 macro void? @abc(int a, int b, int z)
 {