diff --git a/lib/nghttp2_helper.c b/lib/nghttp2_helper.c
index 3b841cc3..dcc70bd0 100644
--- a/lib/nghttp2_helper.c
+++ b/lib/nghttp2_helper.c
@@ -51,21 +51,6 @@ uint32_t nghttp2_get_uint32(const uint8_t *data) {
   return ntohl(n);
 }
 
-void *nghttp2_memdup(const void *src, size_t n, nghttp2_mem *mem) {
-  void *dest;
-
-  if (n == 0) {
-    return NULL;
-  }
-
-  dest = nghttp2_mem_malloc(mem, n);
-  if (dest == NULL) {
-    return NULL;
-  }
-  memcpy(dest, src, n);
-  return dest;
-}
-
 /* Generated by gendowncasetbl.py */
 static const uint8_t DOWNCASE_TBL[] = {
     0 /* NUL  */,   1 /* SOH  */,   2 /* STX  */,   3 /* ETX  */,
diff --git a/lib/nghttp2_helper.h b/lib/nghttp2_helper.h
index 89631823..9e2a71d3 100644
--- a/lib/nghttp2_helper.h
+++ b/lib/nghttp2_helper.h
@@ -67,18 +67,6 @@ uint16_t nghttp2_get_uint16(const uint8_t *data);
  */
 uint32_t nghttp2_get_uint32(const uint8_t *data);
 
-/*
- * Allocates |n| bytes of memory and copy the memory region pointed by
- * |src| with the length |n| bytes into it. Returns the allocated memory.
- *
- * This function returns pointer to allocated memory, or one of the
- * following negative error codes:
- *
- * NGHTTP2_ERR_NOMEM
- *     Out of memory.
- */
-void *nghttp2_memdup(const void *src, size_t n, nghttp2_mem *mem);
-
 void nghttp2_downcase(uint8_t *s, size_t len);
 
 /*