diff --git a/lib/php-calculator-improved.sh b/lib/php-calculator-improved.sh
index 19ec7c8..2940c62 100644
--- a/lib/php-calculator-improved.sh
+++ b/lib/php-calculator-improved.sh
@@ -323,6 +323,11 @@ calculate_server_capacity() {
         available_mb=$max_php_fpm
     fi
 
+    # CRITICAL: Never allow negative available memory
+    if [ "$available_mb" -lt 0 ]; then
+        available_mb=0
+    fi
+
     # Conservative memory per process for safety (20MB)
     local memory_per_process=20