diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index c0bcc1d..3456baa 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -820,6 +820,37 @@
 
 
 ngx_int_t
+ngx_dns_strcmp(u_char *s1, u_char *s2)
+{
+    ngx_uint_t  c1, c2;
+
+    for ( ;; ) {
+        c1 = (ngx_uint_t) *s1++;
+        c2 = (ngx_uint_t) *s2++;
+
+        c1 = (c1 >= 'A' && c1 <= 'Z') ? (c1 | 0x20) : c1;
+        c2 = (c2 >= 'A' && c2 <= 'Z') ? (c2 | 0x20) : c2;
+
+        if (c1 == c2) {
+
+            if (c1) {
+                continue;
+            }
+
+            return 0;
+        }
+
+        /* in ASCII '.' > '-', but we need '.' to be the lowest character */
+
+        c1 = (c1 == '.') ? ' ' : c1;
+        c2 = (c2 == '.') ? ' ' : c2;
+
+        return c1 - c2;
+    }
+}
+
+
+ngx_int_t
 ngx_atoi(u_char *line, size_t n)
 {
     ngx_int_t  value;
diff --git a/src/core/ngx_string.h b/src/core/ngx_string.h
index 81e1ea1..0525b0e 100644
--- a/src/core/ngx_string.h
+++ b/src/core/ngx_string.h
@@ -158,6 +158,7 @@
 ngx_int_t ngx_rstrncmp(u_char *s1, u_char *s2, size_t n);
 ngx_int_t ngx_rstrncasecmp(u_char *s1, u_char *s2, size_t n);
 ngx_int_t ngx_memn2cmp(u_char *s1, u_char *s2, size_t n1, size_t n2);
+ngx_int_t ngx_dns_strcmp(u_char *s1, u_char *s2);
 
 ngx_int_t ngx_atoi(u_char *line, size_t n);
 ssize_t ngx_atosz(u_char *line, size_t n);
diff --git a/src/http/modules/ngx_http_map_module.c b/src/http/modules/ngx_http_map_module.c
index 1f7786c..abdae0d 100644
--- a/src/http/modules/ngx_http_map_module.c
+++ b/src/http/modules/ngx_http_map_module.c
@@ -337,7 +337,7 @@
     first = (ngx_hash_key_t *) one;
     second = (ngx_hash_key_t *) two;
 
-    return ngx_strcmp(first->key.data, second->key.data);
+    return ngx_dns_strcmp(first->key.data, second->key.data);
 }
 
 
diff --git a/src/http/modules/ngx_http_referer_module.c b/src/http/modules/ngx_http_referer_module.c
index 658f4a1..608623f 100644
--- a/src/http/modules/ngx_http_referer_module.c
+++ b/src/http/modules/ngx_http_referer_module.c
@@ -562,5 +562,5 @@
     first = (ngx_hash_key_t *) one;
     second = (ngx_hash_key_t *) two;
 
-    return ngx_strcmp(first->key.data, second->key.data);
+    return ngx_dns_strcmp(first->key.data, second->key.data);
 }
diff --git a/src/http/ngx_http.c b/src/http/ngx_http.c
index b091515..f5cb430 100644
--- a/src/http/ngx_http.c
+++ b/src/http/ngx_http.c
@@ -1601,7 +1601,7 @@
     first = (ngx_hash_key_t *) one;
     second = (ngx_hash_key_t *) two;
 
-    return ngx_strcmp(first->key.data, second->key.data);
+    return ngx_dns_strcmp(first->key.data, second->key.data);
 }