diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index 45079b7..0385c96 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -503,6 +503,40 @@
 }
 
 
+u_char *
+ngx_strnstr(u_char *s1, char *s2, size_t len)
+{
+    u_char  c1, c2;
+    size_t  n;
+
+    c2 = *(u_char *) s2++;
+
+    n = ngx_strlen(s2);
+
+    do {
+        do {
+            if (len-- == 0) {
+                return NULL;
+            }
+
+            c1 = *s1++;
+
+            if (c1 == 0) {
+                return NULL;
+            }
+
+        } while (c1 != c2);
+
+        if (n > len) {
+            return NULL;
+        }
+
+    } while (ngx_strncmp(s1, (u_char *) s2, n) != 0);
+
+    return --s1;
+}
+
+
 /*
  * ngx_strstrn() and ngx_strcasestrn() are intended to search for static
  * substring with known length in null-terminated string. The argument n
diff --git a/src/core/ngx_string.h b/src/core/ngx_string.h
index e17fc13..3199384 100644
--- a/src/core/ngx_string.h
+++ b/src/core/ngx_string.h
@@ -126,6 +126,8 @@
 ngx_int_t ngx_strcasecmp(u_char *s1, u_char *s2);
 ngx_int_t ngx_strncasecmp(u_char *s1, u_char *s2, size_t n);
 
+u_char *ngx_strnstr(u_char *s1, char *s2, size_t n);
+
 u_char *ngx_strstrn(u_char *s1, char *s2, size_t n);
 u_char *ngx_strcasestrn(u_char *s1, char *s2, size_t n);