diff --git a/core/polyfills.php b/core/polyfills.php
index 2102d7d0..26231298 100644
--- a/core/polyfills.php
+++ b/core/polyfills.php
@@ -511,6 +511,24 @@ function no_escape(string $input): string
     return $input;
 }
 
+/**
+ * Given a 1-indexed numeric-ish thing, return a zero-indexed
+ * number between 0 and $max
+ */
+function page_number(string $input, ?int $max=null): int
+{
+    if (!is_numeric($input)) {
+        $pageNumber = 0;
+    } elseif ($input <= 0) {
+        $pageNumber = 0;
+    } elseif (!is_null($max) && $input >= $max) {
+        $pageNumber = $max - 1;
+    } else {
+        $pageNumber = $input - 1;
+    }
+    return $pageNumber;
+}
+
 function clamp(?int $val, ?int $min=null, ?int $max=null): int
 {
     if (!is_numeric($val) || (!is_null($min) && $val < $min)) {
diff --git a/ext/forum/main.php b/ext/forum/main.php
index 95945df4..5906488f 100644
--- a/ext/forum/main.php
+++ b/ext/forum/main.php
@@ -249,19 +249,10 @@ class Forum extends Extension
     {
         global $config, $database;
         $threadsPerPage = $config->get_int('forumThreadsPerPage', 15);
-        $totalPages = ceil($database->get_one("SELECT COUNT(*) FROM forum_threads") / $threadsPerPage);
+        $totalPages = (int)ceil($database->get_one("SELECT COUNT(*) FROM forum_threads") / $threadsPerPage);
 
         if ($event->count_args() >= 2) {
-            $pageNumber = $event->get_arg(1);
-            if (!is_numeric($pageNumber)) {
-                $pageNumber = 0;
-            } elseif ($pageNumber <= 0) {
-                $pageNumber = 0;
-            } elseif ($pageNumber >= $totalPages) {
-                $pageNumber = $totalPages - 1;
-            } else {
-                $pageNumber--;
-            }
+            $pageNumber = page_number($event->get_arg(1), $totalPages);
         } else {
             $pageNumber = 0;
         }
@@ -286,20 +277,11 @@ class Forum extends Extension
         global $config, $database;
         $threadID = int_escape($event->get_arg(1));
         $postsPerPage = $config->get_int('forumPostsPerPage', 15);
-        $totalPages = ceil($database->get_one("SELECT COUNT(*) FROM forum_posts WHERE thread_id = :id", ['id'=>$threadID]) / $postsPerPage);
+        $totalPages = (int)ceil($database->get_one("SELECT COUNT(*) FROM forum_posts WHERE thread_id = :id", ['id'=>$threadID]) / $postsPerPage);
         $threadTitle = $this->get_thread_title($threadID);
 
         if ($event->count_args() >= 3) {
-            $pageNumber = $event->get_arg(2);
-            if (!is_numeric($pageNumber)) {
-                $pageNumber = 0;
-            } elseif ($pageNumber <= 0) {
-                $pageNumber = 0;
-            } elseif ($pageNumber >= $totalPages) {
-                $pageNumber = $totalPages - 1;
-            } else {
-                $pageNumber--;
-            }
+            $pageNumber = page_number($event->get_arg(2), $totalPages);
         } else {
             $pageNumber = 0;
         }
diff --git a/ext/pools/main.php b/ext/pools/main.php
index 57755648..447d19a4 100644
--- a/ext/pools/main.php
+++ b/ext/pools/main.php
@@ -237,7 +237,7 @@ class Pools extends Extension
                     break;
 
                 case "updated":
-                    $this->get_history(int_escape($event->get_arg(1)));
+                    $this->get_history(page_number($event->get_arg(1)));
                     break;
 
                 case "revert":
@@ -832,14 +832,6 @@ class Pools extends Extension
     {
         global $config, $database;
 
-        if (is_null($pageNumber) || !is_numeric($pageNumber)) {
-            $pageNumber = 0;
-        } elseif ($pageNumber <= 0) {
-            $pageNumber = 0;
-        } else {
-            $pageNumber--;
-        }
-
         $historiesPerPage = $config->get_int(PoolsConfig::UPDATED_PER_PAGE);
 
         $history = $database->get_all("