diff -ruN a/naxsi_src/naxsi.h b/naxsi_src/naxsi.h
--- a/naxsi_src/naxsi.h	2022-09-15 10:40:24.571506605 +0200
+++ b/naxsi_src/naxsi.h	2022-09-15 11:00:20.373150396 +0200
@@ -496,6 +496,17 @@
 #define LIBINJ_SQL_T "d:libinj_sql"
 #define NEGATIVE_T   "negative"
 
+#if defined nginx_version && (nginx_version >= 1021005)
+// after 1.21.5 NGX_REGEX_MULTILINE is present.
+#define NAXSI_REGEX_OPTIONS (NGX_REGEX_CASELESS | NGX_REGEX_MULTILINE)
+#else
+#if (NGX_PCRE2)
+#define NAXSI_REGEX_OPTIONS (PCRE2_CASELESS | PCRE2_MULTILINE)
+#else
+#define NAXSI_REGEX_OPTIONS (PCRE_CASELESS | PCRE_MULTILINE)
+#endif
+#endif
+
 /*
 ** name of hardcoded variables to
 ** change behavior of naxsi at runtime
diff -ruN a/naxsi_src/naxsi_config.c b/naxsi_src/naxsi_config.c
--- a/naxsi_src/naxsi_config.c	2022-09-15 10:28:25.718622978 +0200
+++ b/naxsi_src/naxsi_config.c	2022-09-15 11:16:02.981061190 +0200
@@ -322,11 +322,8 @@
 
         custom_rule->target_rx = ngx_pcalloc(r->pool, sizeof(ngx_regex_compile_t));
         return_value_if(!custom_rule->target_rx, NGX_CONF_ERROR);
-#if (NGX_PCRE2)
-        custom_rule->target_rx->options  = PCRE2_CASELESS | PCRE2_MULTILINE;
-#else
-        custom_rule->target_rx->options  = PCRE_CASELESS | PCRE_MULTILINE;
-#endif
+
+        custom_rule->target_rx->options  = NAXSI_REGEX_OPTIONS;
         custom_rule->target_rx->pattern  = custom_rule->target;
         custom_rule->target_rx->pool     = r->pool;
         custom_rule->target_rx->err.len  = 0;
@@ -445,11 +442,8 @@
   ha.len  = tmp->len - strlen(RX_T);
   rgc     = ngx_pcalloc(r->pool, sizeof(ngx_regex_compile_t));
   return_value_if(!rgc, NGX_CONF_ERROR);
-#if (NGX_PCRE2)
-  rgc->options  = PCRE2_CASELESS | PCRE2_MULTILINE;
-#else
-  rgc->options  = PCRE_CASELESS | PCRE_MULTILINE;
-#endif
+
+  rgc->options  = NAXSI_REGEX_OPTIONS;
   rgc->pattern  = ha;
   rgc->pool     = r->pool;
   rgc->err.len  = 0;
diff -ruN a/naxsi_src/naxsi_utils.c b/naxsi_src/naxsi_utils.c
--- a/naxsi_src/naxsi_utils.c	2022-09-15 10:30:01.476347741 +0200
+++ b/naxsi_src/naxsi_utils.c	2022-09-15 11:16:47.700012002 +0200
@@ -800,11 +800,7 @@
             ngx_pcalloc(cf->pool, sizeof(ngx_regex_compile_t));
           rgc = custloc_array(curr_r->br->custom_locations->elts)[name_idx].target_rx;
           if (rgc) {
-#if (NGX_PCRE2)
-            rgc->options  = PCRE2_CASELESS | PCRE2_MULTILINE;
-#else
-            rgc->options  = PCRE_CASELESS | PCRE_MULTILINE;
-#endif
+            rgc->options  = NAXSI_REGEX_OPTIONS;
             rgc->pattern  = custloc_array(curr_r->br->custom_locations->elts)[name_idx].target;
             rgc->pool     = cf->pool;
             rgc->err.len  = 0;
@@ -820,11 +816,7 @@
             ngx_pcalloc(cf->pool, sizeof(ngx_regex_compile_t));
           rgc = custloc_array(curr_r->br->custom_locations->elts)[uri_idx].target_rx;
           if (rgc) {
-#if (NGX_PCRE2)
-            rgc->options  = PCRE2_CASELESS | PCRE2_MULTILINE;
-#else
-            rgc->options  = PCRE_CASELESS | PCRE_MULTILINE;
-#endif
+            rgc->options  = NAXSI_REGEX_OPTIONS;
             rgc->pattern  = custloc_array(curr_r->br->custom_locations->elts)[uri_idx].target;
             rgc->pool     = cf->pool;
             rgc->err.len  = 0;