diff --git a/src/Psalm/CodeLocation.php b/src/Psalm/CodeLocation.php
index 588a83230e5..90c612bacf8 100644
--- a/src/Psalm/CodeLocation.php
+++ b/src/Psalm/CodeLocation.php
@@ -14,8 +14,8 @@
 use function strlen;
 use function strpos;
 use function strrpos;
-use function substr;
 use function substr_count;
+use function mb_strcut;
 use function trim;
 
 class CodeLocation
@@ -183,7 +183,7 @@ private function calculateRealLocation(): void
         ) {
             $preview_lines = explode(
                 "\n",
-                substr(
+                mb_strcut(
                     $file_contents,
                     $this->preview_start,
                     $this->selection_start - $this->preview_start - 1
@@ -206,7 +206,7 @@ private function calculateRealLocation(): void
 
             $indentation = (int)strpos($key_line, '@');
 
-            $key_line = trim(preg_replace('@\**/\s*@', '', substr($key_line, $indentation)));
+            $key_line = trim(preg_replace('@\**/\s*@', '', mb_strcut($key_line, $indentation)));
 
             $this->selection_start = $preview_offset + $indentation + $this->preview_start;
             $this->selection_end = $this->selection_start + strlen($key_line);
@@ -258,7 +258,7 @@ private function calculateRealLocation(): void
                     throw new \UnexpectedValueException('Unrecognised regex type ' . $this->regex_type);
             }
 
-            $preview_snippet = substr(
+            $preview_snippet = mb_strcut(
                 $file_contents,
                 $this->selection_start,
                 $this->selection_end - $this->selection_start
@@ -298,8 +298,8 @@ private function calculateRealLocation(): void
             }
         }
 
-        $this->snippet = substr($file_contents, $this->preview_start, $this->preview_end - $this->preview_start);
-        $this->text = substr($file_contents, $this->selection_start, $this->selection_end - $this->selection_start);
+        $this->snippet = mb_strcut($file_contents, $this->preview_start, $this->preview_end - $this->preview_start);
+        $this->text = mb_strcut($file_contents, $this->selection_start, $this->selection_end - $this->selection_start);
 
         // reset preview start to beginning of line
         $this->column_from = $this->selection_start -
diff --git a/src/Psalm/Internal/Json/Json.php b/src/Psalm/Internal/Json/Json.php
index b62130a0f8c..66ec0cb8a54 100644
--- a/src/Psalm/Internal/Json/Json.php
+++ b/src/Psalm/Internal/Json/Json.php
@@ -4,6 +4,7 @@
 use RuntimeException;
 
 use function json_encode;
+use function json_last_error_msg;
 use const JSON_PRETTY_PRINT;
 use const JSON_UNESCAPED_SLASHES;
 use const JSON_UNESCAPED_UNICODE;
@@ -34,7 +35,8 @@ public static function encode($data, ?int $options = null): string
 
         $result = json_encode($data, $options);
         if ($result === false) {
-            throw new RuntimeException('Cannot create JSON string.');
+            /** @psalm-suppress ImpureFunctionCall */
+            throw new RuntimeException('Cannot create JSON string: '.json_last_error_msg());
         }
 
         return $result;
diff --git a/src/Psalm/Type/Atomic/TLiteralString.php b/src/Psalm/Type/Atomic/TLiteralString.php
index 5c585923656..fc17b001248 100644
--- a/src/Psalm/Type/Atomic/TLiteralString.php
+++ b/src/Psalm/Type/Atomic/TLiteralString.php
@@ -2,8 +2,8 @@
 namespace Psalm\Type\Atomic;
 
 use function preg_replace;
-use function strlen;
-use function substr;
+use function mb_strlen;
+use function mb_substr;
 
 /**
  * Denotes a string whose value is known.
@@ -31,8 +31,8 @@ public function __toString(): string
     public function getId(bool $nested = false): string
     {
         $no_newline_value = preg_replace("/\n/m", '\n', $this->value);
-        if (strlen($this->value) > 80) {
-            return '"' . substr($no_newline_value, 0, 80) . '...' . '"';
+        if (mb_strlen($this->value) > 80) {
+            return '"' . mb_substr($no_newline_value, 0, 80) . '...' . '"';
         }
 
         return '"' . $no_newline_value . '"';
diff --git a/tests/TypeParseTest.php b/tests/TypeParseTest.php
index 600c5e15651..590ca37d5ef 100644
--- a/tests/TypeParseTest.php
+++ b/tests/TypeParseTest.php
@@ -3,10 +3,11 @@
 
 use function function_exists;
 use function print_r;
+use function mb_substr;
+use function stripos;
 
 use Psalm\Internal\RuntimeCaches;
 use Psalm\Type;
-use function stripos;
 
 class TypeParseTest extends TestCase
 {
@@ -860,6 +861,15 @@ public function testEnumWithoutSpaces(): void
         $this->assertSame($resolved_type->getId(), $docblock_type->getId());
     }
 
+    public function testLongUtf8LiteralString(): void
+    {
+        $string = "АаБбВвГгДдЕеЁёЖжЗзИиЙйКкЛлМмНнОоПпРрСсТтУуФфХхЦцЧчШшЩщЪъЫыЬьЭэЮюЯя";
+        $string .= $string;
+        $expected = mb_substr($string, 0, 80);
+        $this->assertSame("\"$expected...\"", Type:: parseString("'$string'")->getId());
+        $this->assertSame("\"$expected...\"", Type:: parseString("\"$string\"")->getId());
+    }
+
     public function testSingleLiteralString(): void
     {
         $this->assertSame(