diff --git a/ibm_db2.c b/ibm_db2.c
index 89be662..55af753 100644
--- a/ibm_db2.c
+++ b/ibm_db2.c
@@ -4038,6 +4038,11 @@ PHP_FUNCTION(db2_exec)
         return;
     }
 
+    if (!stmt_string || stmt_string_len < 1) {
+        zend_argument_value_error(2, "must be a non-empty string");
+        return;
+    }
+
     if (connection) {
         ZEND_FETCH_RESOURCE_2(conn_res, conn_handle*, &connection, connection_id,
             "Connection Resource", le_conn_struct, le_pconn_struct);
@@ -4130,6 +4135,11 @@ PHP_FUNCTION(db2_prepare)
         return;
     }
 
+    if (!stmt_string || stmt_string_len < 1) {
+        zend_argument_value_error(2, "must be a non-empty string");
+        return;
+    }
+
     if (connection) {
         ZEND_FETCH_RESOURCE_2(conn_res, conn_handle*, &connection, connection_id,
             "Connection Resource", le_conn_struct, le_pconn_struct);