diff --git a/core/polyfills.php b/core/polyfills.php
index 6e5bc820..d9040ee1 100644
--- a/core/polyfills.php
+++ b/core/polyfills.php
@@ -431,25 +431,26 @@ function clamp(int $val, ?int $min = null, ?int $max = null): int
     return $val;
 }
 
-/**
- * Original PHP code by Chirp Internet: www.chirp.com.au
- * Please acknowledge use of this code by including this header.
- */
 function truncate(string $string, int $limit, string $break = " ", string $pad = "..."): string
 {
-    // return with no change if string is shorter than $limit
-    if (strlen($string) <= $limit) {
+    $e = "UTF-8";
+    $strlen = mb_strlen($string, $e);
+    $padlen = mb_strlen($pad, $e);
+    assert($limit > $padlen, "Can't truncate to a length less than the padding length");
+
+    // if string is shorter or equal to limit, leave it alone
+    if($strlen <= $limit) {
         return $string;
     }
 
-    // is $break present between $limit and the end of the string?
-    if (false !== ($breakpoint = strpos($string, $break, $limit))) {
-        if ($breakpoint < strlen($string) - 1) {
-            $string = substr($string, 0, $breakpoint) . $pad;
-        }
+    // if there is a break point between 0 and $limit, truncate to that
+    $breakpoint = mb_strrpos($string, $break, -($strlen - $limit + $padlen), $e);
+    if ($breakpoint !== false) {
+        return mb_substr($string, 0, $breakpoint, $e) . $pad;
     }
 
-    return $string;
+    // if there is no break point, cut mid-word
+    return mb_substr($string, 0, $limit - $padlen, $e) . $pad;
 }
 
 /**
diff --git a/core/tests/PolyfillsTest.php b/core/tests/PolyfillsTest.php
index 2ca5328f..03f95fe6 100644
--- a/core/tests/PolyfillsTest.php
+++ b/core/tests/PolyfillsTest.php
@@ -85,10 +85,11 @@ class PolyfillsTest extends TestCase
 
     public function test_truncate(): void
     {
-        $this->assertEquals("test words", truncate("test words", 10));
-        $this->assertEquals("test...", truncate("test...", 9));
-        $this->assertEquals("test...", truncate("test...", 6));
-        $this->assertEquals("te...", truncate("te...", 2));
+        $this->assertEquals("test words", truncate("test words", 10), "No truncation if string is short enough");
+        $this->assertEquals("test...", truncate("test words", 9), "Truncate when string is too long");
+        $this->assertEquals("test...", truncate("test words", 7), "Truncate to the same breakpoint");
+        $this->assertEquals("te...", truncate("test words", 5), "Breakpoints past the limit don't matter");
+        $this->assertEquals("o...", truncate("oneVeryLongWord", 4), "Hard-break if there are no breakpoints");
     }
 
     public function test_to_shorthand_int(): void
diff --git a/ext/comment/theme.php b/ext/comment/theme.php
index 9cbdc108..adf39848 100644
--- a/ext/comment/theme.php
+++ b/ext/comment/theme.php
@@ -210,7 +210,7 @@ class CommentListTheme extends Themelet
         $h_name = html_escape($comment->owner_name);
         $h_timestamp = autodate($comment->posted);
         if ($trim) {
-            $h_comment = strlen($tfe->stripped) > 52 ? substr($tfe->stripped, 0, 50)."..." : $tfe->stripped;
+            $h_comment = truncate($tfe->stripped, 50);
         } else {
             $h_comment = $tfe->formatted;
         }
diff --git a/ext/forum/theme.php b/ext/forum/theme.php
index ea7400f8..c530cfec 100644
--- a/ext/forum/theme.php
+++ b/ext/forum/theme.php
@@ -226,13 +226,7 @@ class ForumTheme extends Themelet
 
         foreach ($threads as $thread) {
             $titleSubString = $config->get_int('forumTitleSubString');
-
-            if ($titleSubString < strlen($thread["title"])) {
-                $title = substr($thread["title"], 0, $titleSubString);
-                $title = $title."...";
-            } else {
-                $title = $thread["title"];
-            }
+            $title = truncate($thread["title"], $titleSubString);
 
             $tbody->appendChild(
                 TR(
diff --git a/themes/danbooru/comment.theme.php b/themes/danbooru/comment.theme.php
index 8214b9d9..73caabc6 100644
--- a/themes/danbooru/comment.theme.php
+++ b/themes/danbooru/comment.theme.php
@@ -104,7 +104,7 @@ class CustomCommentListTheme extends CommentListTheme
         $h_name = html_escape($comment->owner_name);
         //$h_poster_ip = html_escape($comment->poster_ip);
         if ($trim) {
-            $h_comment = strlen($tfe->stripped) > 52 ? substr($tfe->stripped, 0, 50)."..." : $tfe->stripped;
+            $h_comment = truncate($tfe->stripped, 50);
         } else {
             $h_comment = $tfe->formatted;
         }
diff --git a/themes/danbooru2/comment.theme.php b/themes/danbooru2/comment.theme.php
index 59bd1143..2d365088 100644
--- a/themes/danbooru2/comment.theme.php
+++ b/themes/danbooru2/comment.theme.php
@@ -104,7 +104,7 @@ class CustomCommentListTheme extends CommentListTheme
         $h_name = html_escape($comment->owner_name);
         //$h_poster_ip = html_escape($comment->poster_ip);
         if ($trim) {
-            $h_comment = strlen($tfe->stripped) > 52 ? substr($tfe->stripped, 0, 50)."..." : $tfe->stripped;
+            $h_comment = truncate($tfe->stripped, 50);
         } else {
             $h_comment = $tfe->formatted;
         }
diff --git a/themes/futaba/comment.theme.php b/themes/futaba/comment.theme.php
index 0335e032..c4ea8c88 100644
--- a/themes/futaba/comment.theme.php
+++ b/themes/futaba/comment.theme.php
@@ -78,7 +78,7 @@ class CustomCommentListTheme extends CommentListTheme
         $h_name = html_escape($comment->owner_name);
         //$h_poster_ip = html_escape($comment->poster_ip);
         if ($trim) {
-            $h_comment = strlen($tfe->stripped) > 52 ? substr($tfe->stripped, 0, 50)."..." : $tfe->stripped;
+            $h_comment = truncate($tfe->stripped, 50);
         } else {
             $h_comment = $tfe->formatted;
         }