diff --git a/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php b/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php
index d19e264e3..b4eee08a6 100644
--- a/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php
@@ -1449,9 +1449,20 @@ class ProjectAnalyzer
             return 1;
         }
 
-        $has_nproc = trim((string) @shell_exec('command -v nproc'));
-        if ($has_nproc) {
-            $ret = @shell_exec('nproc');
+        if (\function_exists('shell_exec')) {
+            $has_nproc = trim((string) @shell_exec('command -v nproc'));
+            if ($has_nproc) {
+                $ret = @shell_exec('nproc');
+                if (is_string($ret)) {
+                    $ret = trim($ret);
+                    $tmp = filter_var($ret, FILTER_VALIDATE_INT);
+                    if (is_int($tmp)) {
+                        return $tmp;
+                    }
+                }
+            }
+
+            $ret = @shell_exec('sysctl -n hw.ncpu');
             if (is_string($ret)) {
                 $ret = trim($ret);
                 $tmp = filter_var($ret, FILTER_VALIDATE_INT);
@@ -1461,15 +1472,6 @@ class ProjectAnalyzer
             }
         }
 
-        $ret = @shell_exec('sysctl -n hw.ncpu');
-        if (is_string($ret)) {
-            $ret = trim($ret);
-            $tmp = filter_var($ret, FILTER_VALIDATE_INT);
-            if (is_int($tmp)) {
-                return $tmp;
-            }
-        }
-
         if (is_readable('/proc/cpuinfo')) {
             $cpuinfo = file_get_contents('/proc/cpuinfo');
             $count = substr_count($cpuinfo, 'processor');