diff -u b/core/modules/comment/comment.module b/core/modules/comment/comment.module
--- b/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -1046,7 +1046,7 @@
 function comment_cron() {
   // Store the maximum possible comments per thread (used for node search
   // ranking by reply count).
-  \Drupal::state()->set('comment.node_comment_statistics_scale', 1.0 / max(1.0, (float) db_query('SELECT MAX(comment_count) FROM {comment_entity_statistics}')->fetchField()));
+  \Drupal::state()->set('comment.node_comment_statistics_scale', 1.0 / max(1, db_query('SELECT MAX(comment_count) FROM {comment_entity_statistics}')->fetchField()));
 }
 
 /**
@@ -1056,8 +1056,8 @@
  */
 function comment_cron() {
   // Store the maximum possible comments per thread (used for node search
-  // ranking by reply count).
-  \Drupal::state()->set('comment.node_comment_statistics_scale', 1.0 / max(1, db_query('SELECT MAX(comment_count) FROM {comment_entity_statistics}')->fetchField()));
+  // ranking by reply count). Make sure it is a float value.
+  \Drupal::state()->set('comment.node_comment_statistics_scale', 1.0 / max(1.0, (float) db_query('SELECT MAX(comment_count) FROM {comment_entity_statistics}')->fetchField()));
 }
 
 /**
@@ -1558,8 +1558,8 @@
         'on' => "ces.entity_id = i.sid AND ces.entity_type = 'node' AND ces.field_id = 'node__comment'",
       ),
       // Inverse law that maps the highest reply count on the site to 1 and 0 to 0.
-      'score' => '2.0 - 2.0 / (1.0 + ces.comment_count * (CAST (:comment_scale AS DECIMAL(10, 4))))',
-      'arguments' => array(':comment_scale' => \Drupal::state()->get('comment.node_comment_statistics_scale') ?: 0),
+      'score' => '2.0 - 2.0 / (1.0 + ces.comment_count * :scale)',
+      'arguments' => array(':scale' => (float) \Drupal::state()->get('comment.node_comment_statistics_scale') ?: 0),
     ),
   );
 }
@@ -1569,9 +1569,12 @@
         // nodes.
         'on' => "ces.entity_id = i.sid AND ces.entity_type = 'node' AND ces.field_id = 'node__comment'",
       ),
-      // Inverse law that maps the highest reply count on the site to 1 and 0 to 0.
-      'score' => '2.0 - 2.0 / (1.0 + ces.comment_count * :scale)',
-      'arguments' => array(':scale' => (float) \Drupal::state()->get('comment.node_comment_statistics_scale') ?: 0),
+      // Inverse law that maps the highest reply count on the site to 1 and 0
+      // to 0. Note that the CAST here is necessary for PostgreSQL, because the
+      // PostgreSQL PDO driver sometimes puts values in as strings instead of
+      // numbers in complex expressions like this.
+      'score' => '2.0 - 2.0 / (1.0 + ces.comment_count * (CAST (:comment_scale AS DECIMAL(10, 4))))',
+      'arguments' => array(':comment_scale' => \Drupal::state()->get('comment.node_comment_statistics_scale') ?: 0),
     ),
   );
 }
diff -u b/core/modules/statistics/statistics.module b/core/modules/statistics/statistics.module
--- b/core/modules/statistics/statistics.module
+++ b/core/modules/statistics/statistics.module
@@ -119,7 +119,8 @@
     \Drupal::state()->set('statistics.day_timestamp', REQUEST_TIME);
   }
 
-  // Calculate the maximum of node views, for node search ranking.
+  // Calculate the maximum of node views, for node search ranking. Make sure
+  // it is a float value.
   \Drupal::state()->set('statistics.node_counter_scale', 1.0 / max(1.0, (float) db_query('SELECT MAX(totalcount) FROM {node_counter}')->fetchField()));
 }
 
@@ -243,7 +244,10 @@
           'alias' => 'node_counter',
           'on' => 'node_counter.nid = i.sid',
         ),
-        // Inverse law that maps the highest view count on the site to 1 and 0 to 0.
+        // Inverse law that maps the highest view count on the site to 1 and 0
+        // to 0. Note that the CAST here is necessary for PostgreSQL, because
+        // the PostgreSQL PDO driver sometimes puts values in as strings
+        // instead of numbers in complex expressions like this.
         'score' => '2.0 - 2.0 / (1.0 + node_counter.totalcount * (CAST (:statistics_scale AS DECIMAL(10,4))))',
         'arguments' => array(':statistics_scale' => \Drupal::state()->get('statistics.node_counter_scale') ?: 0),
       ),