diff --git a/src/Psalm/Internal/Codebase/Functions.php b/src/Psalm/Internal/Codebase/Functions.php
index c0a9ae7ce..fa7b0720c 100644
--- a/src/Psalm/Internal/Codebase/Functions.php
+++ b/src/Psalm/Internal/Codebase/Functions.php
@@ -271,7 +271,7 @@ class Functions
             'chdir', 'chgrp', 'chmod', 'chown', 'chroot', 'closedir', 'copy', 'file_put_contents',
             'fopen', 'fread', 'fwrite', 'fclose', 'touch', 'fpassthru', 'fputs', 'fscanf', 'fseek',
             'ftruncate', 'fprintf', 'symlink', 'mkdir', 'unlink', 'rename', 'rmdir', 'popen', 'pclose',
-            'fputcsv',
+            'fputcsv', 'umask',
 
             // stream/socket io
             'stream_context_set_option', 'socket_write', 'stream_set_blocking', 'socket_close',
@@ -296,8 +296,9 @@ class Functions
             'curl_setopt', 'curl_close', 'curl_multi_add_handle', 'curl_multi_remove_handle',
             'curl_multi_select', 'curl_multi_close', 'curl_setopt_array',
 
-            // apc
-            'apc_store', 'apc_delete', 'apcu_store', 'apcu_delete', 'apc_clear_cache',
+            // apc, apcu
+            'apc_store', 'apc_delete', 'apc_clear_cache', 'apc_add', 'apc_inc', 'apc_dec', 'apc_cas',
+            'apcu_store', 'apcu_delete', 'apcu_clear_cache', 'apcu_add', 'apcu_inc', 'apcu_dec', 'apcu_cas',
 
             // newrelic
             'newrelic_start_transaction', 'newrelic_name_transaction', 'newrelic_add_custom_parameter',
diff --git a/tests/UnusedCodeTest.php b/tests/UnusedCodeTest.php
index 779f426ed..4b2f906d8 100644
--- a/tests/UnusedCodeTest.php
+++ b/tests/UnusedCodeTest.php
@@ -246,6 +246,11 @@ class UnusedCodeTest extends TestCase
 
                     foo(4);',
             ],
+            'usedFunctionCall' => [
+                '<?php
+                    $a = strlen("goodbye");
+                    echo $a;',
+            ],
             'possiblyUnusedParamWithUnderscore' => [
                 '<?php
                     class A {
@@ -645,6 +650,11 @@ class UnusedCodeTest extends TestCase
                     (new C)->bar();',
                 'error_message' => 'PossiblyUnusedMethod',
             ],
+            'unusedFunctionCall' => [
+                '<?php
+                    strlen("goodbye");',
+                'error_message' => 'UnusedFunctionCall',
+            ],
             'propertyOverriddenDownstreamAndNotUsed' => [
                 '<?php
                     class A {