diff --git a/builtin/core.wren b/builtin/core.wren
index 3dd35156..77937448 100644
--- a/builtin/core.wren
+++ b/builtin/core.wren
@@ -130,6 +130,7 @@ class WhereSequence is Sequence {
 
 class String is Sequence {
   bytes { StringByteSequence.new(this) }
+  codePoints { StringCodePointSequence.new(this) }
 }
 
 class StringByteSequence is Sequence {
@@ -144,6 +145,18 @@ class StringByteSequence is Sequence {
   count { _string.byteCount_ }
 }
 
+class StringCodePointSequence is Sequence {
+  construct new(string) {
+    _string = string
+  }
+
+  [index] { _string.codePointAt_(index) }
+  iterate(iterator) { _string.iterate(iterator) }
+  iteratorValue(iterator) { _string.codePointAt_(iterator) }
+
+  count { _string.count }
+}
+
 class List is Sequence {
   addAll(other) {
     for (element in other) {
diff --git a/doc/site/core/string.markdown b/doc/site/core/string.markdown
index fbc751ac..cc81dd04 100644
--- a/doc/site/core/string.markdown
+++ b/doc/site/core/string.markdown
@@ -45,20 +45,6 @@ It is a runtime error if `codePoint` is not an integer between `0` and
 
 ## Methods
 
-### **byteAt**(index)
-
-Gets the value of the byte at byte offset `index` in the string.
-
-    :::dart
-    IO.print("hello".byteAt(1)) // 101, for "e".
-
-If the index is negative, it counts backwards from the end of the string.
-
-    :::dart
-    IO.print("hello".byteAt(-4)) // 101, for "e".
-
-It is a runtime error if `index` is not an integer or is out of bounds.
-
 ### **bytes**
 
 Gets a [`Sequence`](sequence.html) that can be used to access the raw bytes of
diff --git a/src/vm/wren_core.c b/src/vm/wren_core.c
index 2250f9f1..244fc12c 100644
--- a/src/vm/wren_core.c
+++ b/src/vm/wren_core.c
@@ -144,6 +144,7 @@ static const char* coreLibSource =
 "\n"
 "class String is Sequence {\n"
 "  bytes { StringByteSequence.new(this) }\n"
+"  codePoints { StringCodePointSequence.new(this) }\n"
 "}\n"
 "\n"
 "class StringByteSequence is Sequence {\n"
@@ -158,6 +159,18 @@ static const char* coreLibSource =
 "  count { _string.byteCount_ }\n"
 "}\n"
 "\n"
+"class StringCodePointSequence is Sequence {\n"
+"  construct new(string) {\n"
+"    _string = string\n"
+"  }\n"
+"\n"
+"  [index] { _string.codePointAt_(index) }\n"
+"  iterate(iterator) { _string.iterate(iterator) }\n"
+"  iteratorValue(iterator) { _string.codePointAt_(iterator) }\n"
+"\n"
+"  count { _string.count }\n"
+"}\n"
+"\n"
 "class List is Sequence {\n"
 "  addAll(other) {\n"
 "    for (element in other) {\n"
@@ -1418,7 +1431,7 @@ void wrenInitializeCore(WrenVM* vm)
   PRIMITIVE(vm->stringClass, "[_]", string_subscript);
   PRIMITIVE(vm->stringClass, "byteAt_(_)", string_byteAt);
   PRIMITIVE(vm->stringClass, "byteCount_", string_byteCount);
-  PRIMITIVE(vm->stringClass, "codePointAt(_)", string_codePointAt);
+  PRIMITIVE(vm->stringClass, "codePointAt_(_)", string_codePointAt);
   PRIMITIVE(vm->stringClass, "contains(_)", string_contains);
   PRIMITIVE(vm->stringClass, "count", string_count);
   PRIMITIVE(vm->stringClass, "endsWith(_)", string_endsWith);
diff --git a/src/vm/wren_value.c b/src/vm/wren_value.c
index 3eec04d9..9a86b2b5 100644
--- a/src/vm/wren_value.c
+++ b/src/vm/wren_value.c
@@ -772,8 +772,18 @@ Value wrenStringCodePointAt(WrenVM* vm, ObjString* string, uint32_t index)
 {
   ASSERT(index < string->length, "Index out of bounds.");
   
-  int numBytes = wrenUtf8DecodeNumBytes(string->value[index]);
-  return wrenNewString(vm, string->value + index, numBytes);
+  int codePoint = wrenUtf8Decode((uint8_t*)string->value + index,
+                                 string->length - index);
+  if (codePoint == -1)
+  {
+    // If it isn't a valid UTF-8 sequence, treat it as a single raw byte.
+    char bytes[2];
+    bytes[0] = string->value[index];
+    bytes[1] = '\0';
+    return wrenNewString(vm, bytes, 1);
+  }
+  
+  return wrenStringFromCodePoint(vm, codePoint);
 }
 
 // Uses the Boyer-Moore-Horspool string matching algorithm.
diff --git a/test/core/string/code_point_at.wren b/test/core/string/code_point_at.wren
deleted file mode 100644
index a4ba4319..00000000
--- a/test/core/string/code_point_at.wren
+++ /dev/null
@@ -1,38 +0,0 @@
-// Bytes:           11111
-//        012345678901234
-// Chars: sø mé ஃ  thî ng
-var s = "søméஃthîng"
-
-IO.print(s.codePointAt(0)) // expect: 115
-IO.print(s.codePointAt(1)) // expect: 248
-IO.print(s.codePointAt(2)) // expect: -1
-IO.print(s.codePointAt(3)) // expect: 109
-IO.print(s.codePointAt(4)) // expect: 233
-IO.print(s.codePointAt(5)) // expect: -1
-IO.print(s.codePointAt(6)) // expect: 2947
-IO.print(s.codePointAt(7)) // expect: -1
-IO.print(s.codePointAt(8)) // expect: -1
-IO.print(s.codePointAt(9)) // expect: 116
-IO.print(s.codePointAt(10)) // expect: 104
-IO.print(s.codePointAt(11)) // expect: 238
-IO.print(s.codePointAt(12)) // expect: -1
-IO.print(s.codePointAt(13)) // expect: 110
-IO.print(s.codePointAt(14)) // expect: 103
-
-IO.print(s.codePointAt(-15)) // expect: 115
-IO.print(s.codePointAt(-14)) // expect: 248
-IO.print(s.codePointAt(-13)) // expect: -1
-IO.print(s.codePointAt(-12)) // expect: 109
-IO.print(s.codePointAt(-11)) // expect: 233
-IO.print(s.codePointAt(-10)) // expect: -1
-IO.print(s.codePointAt(-9)) // expect: 2947
-IO.print(s.codePointAt(-8)) // expect: -1
-IO.print(s.codePointAt(-7)) // expect: -1
-IO.print(s.codePointAt(-6)) // expect: 116
-IO.print(s.codePointAt(-5)) // expect: 104
-IO.print(s.codePointAt(-4)) // expect: 238
-IO.print(s.codePointAt(-3)) // expect: -1
-IO.print(s.codePointAt(-2)) // expect: 110
-IO.print(s.codePointAt(-1)) // expect: 103
-
-IO.print("\0".codePointAt(0)) // expect: 0
diff --git a/test/core/string/code_point_at_incomplete.wren b/test/core/string/code_point_at_incomplete.wren
deleted file mode 100644
index b184b1ec..00000000
--- a/test/core/string/code_point_at_incomplete.wren
+++ /dev/null
@@ -1,8 +0,0 @@
-// The first byte of a two-octet sequence.
-IO.print("\xc0".codePointAt(0)) // expect: -1
-
-// The first byte of a three-octet sequence.
-IO.print("\xe0".codePointAt(0)) // expect: -1
-
-// The first two bytes of a three-octet sequence.
-IO.print("\xe0\xae".codePointAt(0)) // expect: -1
diff --git a/test/core/string/code_point_at_not_int.wren b/test/core/string/code_point_at_not_int.wren
deleted file mode 100644
index 2f1f42f3..00000000
--- a/test/core/string/code_point_at_not_int.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.print("string".codePointAt(12.34)) // expect runtime error: Index must be an integer.
diff --git a/test/core/string/code_point_at_not_num.wren b/test/core/string/code_point_at_not_num.wren
deleted file mode 100644
index fc41da89..00000000
--- a/test/core/string/code_point_at_not_num.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.print("string".codePointAt("not num")) // expect runtime error: Index must be a number.
diff --git a/test/core/string/code_point_at_too_large.wren b/test/core/string/code_point_at_too_large.wren
deleted file mode 100644
index 34424ae4..00000000
--- a/test/core/string/code_point_at_too_large.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.print("string".codePointAt(6)) // expect runtime error: Index out of bounds.
diff --git a/test/core/string/code_point_at_too_small.wren b/test/core/string/code_point_at_too_small.wren
deleted file mode 100644
index ac264d15..00000000
--- a/test/core/string/code_point_at_too_small.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.print("string".codePointAt(-7)) // expect runtime error: Index out of bounds.
diff --git a/test/core/string/iterate.wren b/test/core/string/iterate.wren
index e8a5f1d2..6fd3ce3b 100644
--- a/test/core/string/iterate.wren
+++ b/test/core/string/iterate.wren
@@ -22,3 +22,8 @@ IO.print("a\0b\0c".iterate(1)) // expect: 2
 IO.print("a\0b\0c".iterate(2)) // expect: 3
 IO.print("a\0b\0c".iterate(3)) // expect: 4
 IO.print("a\0b\0c".iterate(4)) // expect: false
+
+// Iterates over invalid UTF-8 one byte at a time.
+IO.print("\xef\xf7".iterate(null)) // expect: 0
+IO.print("\xef\xf7".iterate(0)) // expect: 1
+IO.print("\xef\xf7".iterate(1)) // expect: false
diff --git a/test/core/string/iterator_value.wren b/test/core/string/iterator_value.wren
index 6dd1d401..85838310 100644
--- a/test/core/string/iterator_value.wren
+++ b/test/core/string/iterator_value.wren
@@ -2,8 +2,8 @@ var s = "abçd"
 IO.print(s.iteratorValue(0)) // expect: a
 IO.print(s.iteratorValue(1)) // expect: b
 IO.print(s.iteratorValue(2)) // expect: ç
-// Iterator value in middle of UTF sequence is an empty string.
-IO.print(s.iteratorValue(3) == "") // expect: true
+// Iterator value in middle of UTF sequence is the unencoded byte.
+IO.print(s.iteratorValue(3) == "\xa7") // expect: true
 IO.print(s.iteratorValue(4)) // expect: d
 
 // 8-bit clean.
@@ -13,3 +13,7 @@ IO.print(t.iteratorValue(1) == "\0") // expect: true
 IO.print(t.iteratorValue(2) == "b") // expect: true
 IO.print(t.iteratorValue(3) == "\0") // expect: true
 IO.print(t.iteratorValue(4) == "c") // expect: true
+
+// Returns single byte strings for invalid UTF-8 sequences.
+IO.print("\xef\xf7".iteratorValue(0) == "\xef") // expect: true
+IO.print("\xef\xf7".iteratorValue(1) == "\xf7") // expect: true
diff --git a/test/core/string/subscript.wren b/test/core/string/subscript.wren
index 70c740aa..97998efe 100644
--- a/test/core/string/subscript.wren
+++ b/test/core/string/subscript.wren
@@ -27,12 +27,12 @@ IO.print("søméஃthîng"[-1]) // expect: g
 IO.print("søméஃthîng"[-2]) // expect: n
 IO.print("søméஃthîng"[-4]) // expect: î
 
-// If the subscript is in the middle of a UTF-8 sequence, yield an empty string.
-IO.print("søméஃthîng"[2] == "") // expect: true
-IO.print("søméஃthîng"[7] == "") // expect: true
-IO.print("søméஃthîng"[8] == "") // expect: true
-IO.print("søméஃ"[-1] == "") // expect: true
-IO.print("søméஃ"[-2] == "") // expect: true
+// If the subscript is in the middle of a UTF-8 sequence, return the raw byte.
+IO.print("søméஃthîng"[2] == "\xb8") // expect: true
+IO.print("søméஃthîng"[7] == "\xae") // expect: true
+IO.print("søméஃthîng"[8] == "\x83") // expect: true
+IO.print("søméஃ"[-1] == "\x83") // expect: true
+IO.print("søméஃ"[-2] == "\xae") // expect: true
 
 // 8-bit clean.
 IO.print("a\0b\0c"[0] == "a") // expect: true
@@ -40,3 +40,7 @@ IO.print("a\0b\0c"[1] == "\0") // expect: true
 IO.print("a\0b\0c"[2] == "b") // expect: true
 IO.print("a\0b\0c"[3] == "\0") // expect: true
 IO.print("a\0b\0c"[4] == "c") // expect: true
+
+// Returns single byte strings for invalid UTF-8 sequences.
+IO.print("\xef\xf7"[0] == "\xef") // expect: true
+IO.print("\xef\xf7"[1] == "\xf7") // expect: true
diff --git a/test/core/string/subscript_range.wren b/test/core/string/subscript_range.wren
index d78359b8..75277e81 100644
--- a/test/core/string/subscript_range.wren
+++ b/test/core/string/subscript_range.wren
@@ -45,3 +45,5 @@ IO.print("søméஃthîng"[3...10]) // expect: méஃt
 IO.print("søméஃthîng"[2..6]) // expect: méஃ
 IO.print("søméஃthîng"[2...6]) // expect: mé
 IO.print("søméஃthîng"[2...7]) // expect: méஃ
+
+// TODO: Strings including invalid UTF-8.
diff --git a/test/core/string_byte_sequence/count.wren b/test/core/string_byte_sequence/count.wren
index d9634dae..822d0f98 100644
--- a/test/core/string_byte_sequence/count.wren
+++ b/test/core/string_byte_sequence/count.wren
@@ -12,4 +12,4 @@ IO.print("søméஃ".bytes.count) // expect: 9
 IO.print("\0\0\0".bytes.count) // expect: 3
 
 // Invalid UTF-8.
-IO.print("\xef\x00".bytes.count) // expect: 2
+IO.print("\xef\xf7".bytes.count) // expect: 2
diff --git a/test/core/string_code_point_sequence/iterate.wren b/test/core/string_code_point_sequence/iterate.wren
new file mode 100644
index 00000000..f29db020
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterate.wren
@@ -0,0 +1,29 @@
+var codePoints = "abçd".codePoints
+IO.print(codePoints.iterate(null)) // expect: 0
+IO.print(codePoints.iterate(0)) // expect: 1
+IO.print(codePoints.iterate(1)) // expect: 2
+// Skip 3 because that's the middle of the ç sequence.
+IO.print(codePoints.iterate(2)) // expect: 4
+// Iterating from the middle of a UTF-8 sequence goes to the next one.
+IO.print(codePoints.iterate(3)) // expect: 4
+IO.print(codePoints.iterate(4)) // expect: false
+
+// Out of bounds.
+IO.print(codePoints.iterate(123)) // expect: false
+IO.print(codePoints.iterate(-1)) // expect: false
+
+// Nothing to iterate in an empty string.
+IO.print("".codePoints.iterate(null)) // expect: false
+
+// 8-bit clean.
+IO.print("a\0b\0c".codePoints.iterate(null)) // expect: 0
+IO.print("a\0b\0c".codePoints.iterate(0)) // expect: 1
+IO.print("a\0b\0c".codePoints.iterate(1)) // expect: 2
+IO.print("a\0b\0c".codePoints.iterate(2)) // expect: 3
+IO.print("a\0b\0c".codePoints.iterate(3)) // expect: 4
+IO.print("a\0b\0c".codePoints.iterate(4)) // expect: false
+
+// Iterates over invalid UTF-8 one byte at a time.
+IO.print("\xef\xf7".codePoints.iterate(null)) // expect: 0
+IO.print("\xef\xf7".codePoints.iterate(0)) // expect: 1
+IO.print("\xef\xf7".codePoints.iterate(1)) // expect: false
diff --git a/test/core/string_code_point_sequence/iterate_iterator_not_int.wren b/test/core/string_code_point_sequence/iterate_iterator_not_int.wren
new file mode 100644
index 00000000..f51eea5e
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterate_iterator_not_int.wren
@@ -0,0 +1 @@
+"s".codePoints.iterate(1.5) // expect runtime error: Iterator must be an integer.
diff --git a/test/core/string_code_point_sequence/iterate_iterator_not_num.wren b/test/core/string_code_point_sequence/iterate_iterator_not_num.wren
new file mode 100644
index 00000000..309769a1
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterate_iterator_not_num.wren
@@ -0,0 +1 @@
+"s".codePoints.iterate("2") // expect runtime error: Iterator must be a number.
diff --git a/test/core/string_code_point_sequence/iterator_value.wren b/test/core/string_code_point_sequence/iterator_value.wren
new file mode 100644
index 00000000..54af5f1b
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterator_value.wren
@@ -0,0 +1,42 @@
+// Bytes:           11111
+//        012345678901234
+// Chars: sø mé ஃ  thî ng
+var codePoints = "søméஃthîng".codePoints
+
+IO.print(codePoints.iteratorValue(0)) // expect: 115
+IO.print(codePoints.iteratorValue(1)) // expect: 248
+IO.print(codePoints.iteratorValue(2)) // expect: -1
+IO.print(codePoints.iteratorValue(3)) // expect: 109
+IO.print(codePoints.iteratorValue(4)) // expect: 233
+IO.print(codePoints.iteratorValue(5)) // expect: -1
+IO.print(codePoints.iteratorValue(6)) // expect: 2947
+IO.print(codePoints.iteratorValue(7)) // expect: -1
+IO.print(codePoints.iteratorValue(8)) // expect: -1
+IO.print(codePoints.iteratorValue(9)) // expect: 116
+IO.print(codePoints.iteratorValue(10)) // expect: 104
+IO.print(codePoints.iteratorValue(11)) // expect: 238
+IO.print(codePoints.iteratorValue(12)) // expect: -1
+IO.print(codePoints.iteratorValue(13)) // expect: 110
+IO.print(codePoints.iteratorValue(14)) // expect: 103
+
+IO.print(codePoints.iteratorValue(-15)) // expect: 115
+IO.print(codePoints.iteratorValue(-14)) // expect: 248
+IO.print(codePoints.iteratorValue(-13)) // expect: -1
+IO.print(codePoints.iteratorValue(-12)) // expect: 109
+IO.print(codePoints.iteratorValue(-11)) // expect: 233
+IO.print(codePoints.iteratorValue(-10)) // expect: -1
+IO.print(codePoints.iteratorValue(-9)) // expect: 2947
+IO.print(codePoints.iteratorValue(-8)) // expect: -1
+IO.print(codePoints.iteratorValue(-7)) // expect: -1
+IO.print(codePoints.iteratorValue(-6)) // expect: 116
+IO.print(codePoints.iteratorValue(-5)) // expect: 104
+IO.print(codePoints.iteratorValue(-4)) // expect: 238
+IO.print(codePoints.iteratorValue(-3)) // expect: -1
+IO.print(codePoints.iteratorValue(-2)) // expect: 110
+IO.print(codePoints.iteratorValue(-1)) // expect: 103
+
+IO.print("\0".codePoints.iteratorValue(0)) // expect: 0
+
+// Returns -1 for invalid UTF-8 sequences.
+IO.print("\xef\xf7".codePoints.iteratorValue(0)) // expect: -1
+IO.print("\xef\xf7".codePoints.iteratorValue(1)) // expect: -1
diff --git a/test/core/string_code_point_sequence/iterator_value_incomplete.wren b/test/core/string_code_point_sequence/iterator_value_incomplete.wren
new file mode 100644
index 00000000..ebc59184
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterator_value_incomplete.wren
@@ -0,0 +1,8 @@
+// The first byte of a two-octet sequence.
+IO.print("\xc0".codePoints.iteratorValue(0)) // expect: -1
+
+// The first byte of a three-octet sequence.
+IO.print("\xe0".codePoints.iteratorValue(0)) // expect: -1
+
+// The first two bytes of a three-octet sequence.
+IO.print("\xe0\xae".codePoints.iteratorValue(0)) // expect: -1
diff --git a/test/core/string_code_point_sequence/iterator_value_not_int.wren b/test/core/string_code_point_sequence/iterator_value_not_int.wren
new file mode 100644
index 00000000..0f4ed51b
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterator_value_not_int.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints.iteratorValue(12.34)) // expect runtime error: Index must be an integer.
diff --git a/test/core/string_code_point_sequence/iterator_value_not_num.wren b/test/core/string_code_point_sequence/iterator_value_not_num.wren
new file mode 100644
index 00000000..f0c9d4fb
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterator_value_not_num.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints.iteratorValue("not num")) // expect runtime error: Index must be a number.
diff --git a/test/core/string_code_point_sequence/iterator_value_too_large.wren b/test/core/string_code_point_sequence/iterator_value_too_large.wren
new file mode 100644
index 00000000..8e8598c4
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterator_value_too_large.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints.iteratorValue(6)) // expect runtime error: Index out of bounds.
diff --git a/test/core/string_code_point_sequence/iterator_value_too_small.wren b/test/core/string_code_point_sequence/iterator_value_too_small.wren
new file mode 100644
index 00000000..2fd95fa9
--- /dev/null
+++ b/test/core/string_code_point_sequence/iterator_value_too_small.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints.iteratorValue(-7)) // expect runtime error: Index out of bounds.
diff --git a/test/core/string_code_point_sequence/subscript.wren b/test/core/string_code_point_sequence/subscript.wren
new file mode 100644
index 00000000..3e250bcf
--- /dev/null
+++ b/test/core/string_code_point_sequence/subscript.wren
@@ -0,0 +1,42 @@
+// Bytes:           11111
+//        012345678901234
+// Chars: sø mé ஃ  thî ng
+var codePoints = "søméஃthîng".codePoints
+
+IO.print(codePoints[0]) // expect: 115
+IO.print(codePoints[1]) // expect: 248
+IO.print(codePoints[2]) // expect: -1
+IO.print(codePoints[3]) // expect: 109
+IO.print(codePoints[4]) // expect: 233
+IO.print(codePoints[5]) // expect: -1
+IO.print(codePoints[6]) // expect: 2947
+IO.print(codePoints[7]) // expect: -1
+IO.print(codePoints[8]) // expect: -1
+IO.print(codePoints[9]) // expect: 116
+IO.print(codePoints[10]) // expect: 104
+IO.print(codePoints[11]) // expect: 238
+IO.print(codePoints[12]) // expect: -1
+IO.print(codePoints[13]) // expect: 110
+IO.print(codePoints[14]) // expect: 103
+
+IO.print(codePoints[-15]) // expect: 115
+IO.print(codePoints[-14]) // expect: 248
+IO.print(codePoints[-13]) // expect: -1
+IO.print(codePoints[-12]) // expect: 109
+IO.print(codePoints[-11]) // expect: 233
+IO.print(codePoints[-10]) // expect: -1
+IO.print(codePoints[-9]) // expect: 2947
+IO.print(codePoints[-8]) // expect: -1
+IO.print(codePoints[-7]) // expect: -1
+IO.print(codePoints[-6]) // expect: 116
+IO.print(codePoints[-5]) // expect: 104
+IO.print(codePoints[-4]) // expect: 238
+IO.print(codePoints[-3]) // expect: -1
+IO.print(codePoints[-2]) // expect: 110
+IO.print(codePoints[-1]) // expect: 103
+
+IO.print("\0".codePoints[0]) // expect: 0
+
+// Returns -1 for invalid UTF-8 sequences.
+IO.print("\xef\xf7".codePoints[0]) // expect: -1
+IO.print("\xef\xf7".codePoints[1]) // expect: -1
diff --git a/test/core/string_code_point_sequence/subscript_incomplete.wren b/test/core/string_code_point_sequence/subscript_incomplete.wren
new file mode 100644
index 00000000..2a280213
--- /dev/null
+++ b/test/core/string_code_point_sequence/subscript_incomplete.wren
@@ -0,0 +1,8 @@
+// The first byte of a two-octet sequence.
+IO.print("\xc0".codePoints[0]) // expect: -1
+
+// The first byte of a three-octet sequence.
+IO.print("\xe0".codePoints[0]) // expect: -1
+
+// The first two bytes of a three-octet sequence.
+IO.print("\xe0\xae".codePoints[0]) // expect: -1
diff --git a/test/core/string_code_point_sequence/subscript_not_int.wren b/test/core/string_code_point_sequence/subscript_not_int.wren
new file mode 100644
index 00000000..acc7d5bc
--- /dev/null
+++ b/test/core/string_code_point_sequence/subscript_not_int.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints[12.34]) // expect runtime error: Index must be an integer.
diff --git a/test/core/string_code_point_sequence/subscript_not_num.wren b/test/core/string_code_point_sequence/subscript_not_num.wren
new file mode 100644
index 00000000..07dcf851
--- /dev/null
+++ b/test/core/string_code_point_sequence/subscript_not_num.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints["not num"]) // expect runtime error: Index must be a number.
diff --git a/test/core/string_code_point_sequence/subscript_too_large.wren b/test/core/string_code_point_sequence/subscript_too_large.wren
new file mode 100644
index 00000000..fb40d9d7
--- /dev/null
+++ b/test/core/string_code_point_sequence/subscript_too_large.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints[6]) // expect runtime error: Index out of bounds.
diff --git a/test/core/string_code_point_sequence/subscript_too_small.wren b/test/core/string_code_point_sequence/subscript_too_small.wren
new file mode 100644
index 00000000..5928ce7d
--- /dev/null
+++ b/test/core/string_code_point_sequence/subscript_too_small.wren
@@ -0,0 +1 @@
+IO.print("string".codePoints[-7]) // expect runtime error: Index out of bounds.