diff --git a/common/ngx_http_zstd_common.c b/common/ngx_http_zstd_common.c
new file mode 100644
index 0000000..67b895f
--- /dev/null
+++ b/common/ngx_http_zstd_common.c
@@ -0,0 +1,64 @@
+#include "ngx_http_zstd_common.h"
+
+static /* const */ char kEncoding[] = "zstd";
+static const size_t kEncodingLen = 4;
+
+static ngx_int_t check_accept_encoding(ngx_http_request_t* req) {
+  ngx_table_elt_t* accept_encoding_entry;
+  ngx_str_t* accept_encoding;
+  u_char* cursor;
+  u_char* end;
+  u_char before;
+  u_char after;
+
+  accept_encoding_entry = req->headers_in.accept_encoding;
+  if (accept_encoding_entry == NULL) return NGX_DECLINED;
+  accept_encoding = &accept_encoding_entry->value;
+
+  if (accept_encoding->len < kEncodingLen) return NGX_DECLINED;
+
+  cursor = accept_encoding->data;
+  end = cursor + accept_encoding->len;
+  while (1) {
+    u_char digit;
+    /* It would be an idiotic idea to rely on compiler to produce performant
+       binary, that is why we just do -1 at every call site. */
+    cursor = ngx_strcasestrn(cursor, kEncoding, kEncodingLen - 1);
+    if (cursor == NULL) return NGX_DECLINED;
+    before = (cursor == accept_encoding->data) ? ' ' : cursor[-1];
+    cursor += kEncodingLen;
+    after = (cursor >= end) ? ' ' : *cursor;
+    if (before != ',' && before != ' ') continue;
+    if (after != ',' && after != ' ' && after != ';') continue;
+
+    /* Check for ";q=0[.[0[0[0]]]]" */
+    while (*cursor == ' ') cursor++;
+    if (*(cursor++) != ';') break;
+    while (*cursor == ' ') cursor++;
+    if (*(cursor++) != 'q') break;
+    while (*cursor == ' ') cursor++;
+    if (*(cursor++) != '=') break;
+    while (*cursor == ' ') cursor++;
+    if (*(cursor++) != '0') break;
+    if (*(cursor++) != '.') return NGX_DECLINED; /* ;q=0, */
+    digit = *(cursor++);
+    if (digit < '0' || digit > '9') return NGX_DECLINED; /* ;q=0., */
+    if (digit > '0') break;
+    digit = *(cursor++);
+    if (digit < '0' || digit > '9') return NGX_DECLINED; /* ;q=0.0, */
+    if (digit > '0') break;
+    digit = *(cursor++);
+    if (digit < '0' || digit > '9') return NGX_DECLINED; /* ;q=0.00, */
+    if (digit > '0') break;
+    return NGX_DECLINED; /* ;q=0.000 */
+  }
+  return NGX_OK;
+}
+
+ngx_int_t ngx_http_zstd_check_request(ngx_http_request_t* req) {
+  if (req != req->main) return NGX_DECLINED;
+  if (check_accept_encoding(req) != NGX_OK) return NGX_DECLINED;
+  req->gzip_tested = 1;
+  req->gzip_ok = 0;
+  return NGX_OK;
+}
diff --git a/common/ngx_http_zstd_common.h b/common/ngx_http_zstd_common.h
new file mode 100644
index 0000000..ccdb1d3
--- /dev/null
+++ b/common/ngx_http_zstd_common.h
@@ -0,0 +1,8 @@
+#ifndef _NGX_HTTP_ZSTD_COMMON_INCLUDED_
+#define _NGX_HTTP_ZSTD_COMMON_INCLUDED_
+
+#include <ngx_http.h>
+
+ngx_int_t ngx_http_zstd_check_request(ngx_http_request_t* req);
+
+#endif /* _NGX_HTTP_ZSTD_COMMON_INCLUDED_ */
\ No newline at end of file
diff --git a/filter/config b/filter/config
index 2942125..610bbfc 100644
--- a/filter/config
+++ b/filter/config
@@ -98,7 +98,7 @@ fi
 
 NGX_LD_OPT="$ngx_zstd_opt_L $NGX_LD_OPT"
 
-HTTP_ZSTD_SRCS="$ngx_addon_dir/filter/ngx_http_zstd_filter_module.c"
+HTTP_ZSTD_SRCS="$ngx_addon_dir/common/ngx_http_zstd_common.c $ngx_addon_dir/filter/ngx_http_zstd_filter_module.c"
 
 ngx_addon_name=ngx_http_zstd_filter_module
 ngx_module_type=HTTP_FILTER
diff --git a/filter/ngx_http_zstd_filter_module.c b/filter/ngx_http_zstd_filter_module.c
index 50ec55f..998a5fd 100644
--- a/filter/ngx_http_zstd_filter_module.c
+++ b/filter/ngx_http_zstd_filter_module.c
@@ -10,6 +10,8 @@
 
 #include <zstd.h>
 
+#include "../common/ngx_http_zstd_common.h"
+
 
 #define NGX_HTTP_ZSTD_FILTER_COMPRESS       0
 #define NGX_HTTP_ZSTD_FILTER_FLUSH          1
@@ -88,8 +90,6 @@ static ZSTD_CStream *ngx_http_zstd_filter_create_cstream(ngx_http_request_t *r,
     ngx_http_zstd_ctx_t *ctx);
 static ngx_int_t ngx_http_zstd_filter_compress(ngx_http_request_t *r,
     ngx_http_zstd_ctx_t *ctx);
-static ngx_int_t ngx_http_zstd_accept_encoding(ngx_str_t *ae);
-static ngx_int_t ngx_http_zstd_ok(ngx_http_request_t *r);
 static ngx_int_t ngx_http_zstd_filter_init(ngx_conf_t *cf);
 static void * ngx_http_zstd_create_main_conf(ngx_conf_t *cf);
 static char *ngx_http_zstd_init_main_conf(ngx_conf_t *cf, void *conf);
@@ -194,28 +194,49 @@ static ngx_int_t
 ngx_http_zstd_header_filter(ngx_http_request_t *r)
 {
     ngx_table_elt_t           *h;
-    ngx_http_zstd_loc_conf_t  *zlcf;
+    ngx_http_zstd_loc_conf_t  *conf;
     ngx_http_zstd_ctx_t       *ctx;
 
-    zlcf = ngx_http_get_module_loc_conf(r, ngx_http_zstd_filter_module);
+    conf = ngx_http_get_module_loc_conf(r, ngx_http_zstd_filter_module);
 
-    if (!zlcf->enable
-        || (r->headers_out.status != NGX_HTTP_OK
-            && r->headers_out.status != NGX_HTTP_FORBIDDEN
-            && r->headers_out.status != NGX_HTTP_NOT_FOUND)
-       || (r->headers_out.content_encoding
-           && r->headers_out.content_encoding->value.len)
-       || (r->headers_out.content_length_n != -1
-           && r->headers_out.content_length_n < zlcf->min_length)
-       || ngx_http_test_content_type(r, &zlcf->types) == NULL
-       || r->header_only)
-    {
+    /* Filter only if enabled. */
+    if (!conf->enable) {
+        return ngx_http_next_header_filter(r);
+    }
+
+    /* Only compress OK / forbidden / not found responses. */
+    if (r->headers_out.status != NGX_HTTP_OK &&
+        r->headers_out.status != NGX_HTTP_FORBIDDEN &&
+        r->headers_out.status != NGX_HTTP_NOT_FOUND) {
+        return ngx_http_next_header_filter(r);
+    }
+
+    /* Bypass "header only" responses. */
+    if (r->header_only) {
+        return ngx_http_next_header_filter(r);
+    }
+
+    /* Bypass already compressed responses. */
+    if (r->headers_out.content_encoding &&
+        r->headers_out.content_encoding->value.len) {
+        return ngx_http_next_header_filter(r);
+    }
+
+    /* If response size is known, do not compress tiny responses. */
+    if (r->headers_out.content_length_n != -1 &&
+        r->headers_out.content_length_n < conf->min_length) {
+        return ngx_http_next_header_filter(r);
+    }
+
+    /* Compress only certain MIME-typed responses. */
+    if (ngx_http_test_content_type(r, &conf->types) == NULL) {
         return ngx_http_next_header_filter(r);
     }
 
     r->gzip_vary = 1;
 
-    if (ngx_http_zstd_ok(r) != NGX_OK) {
+    /* Check if client support zstd encoding. */
+    if (ngx_http_zstd_check_request(r) != NGX_OK) {
         return ngx_http_next_header_filter(r);
     }
 
@@ -229,12 +250,17 @@ ngx_http_zstd_header_filter(ngx_http_request_t *r)
     ctx->request = r;
     ctx->last_out = &ctx->out;
 
+    /* Prepare response headers, so that following filters in the chain will
+     notice that response body is compressed. */
     h = ngx_list_push(&r->headers_out.headers);
     if (h == NULL) {
         return NGX_ERROR;
     }
 
     h->hash = 1;
+#if nginx_version >= 1023000
+    h->next = NULL;
+#endif
     ngx_str_set(&h->key, "Content-Encoding");
     ngx_str_set(&h->value, "zstd");
     r->headers_out.content_encoding = h;
@@ -248,7 +274,6 @@ ngx_http_zstd_header_filter(ngx_http_request_t *r)
     return ngx_http_next_header_filter(r);
 }
 
-
 static ngx_int_t
 ngx_http_zstd_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
 {
@@ -654,61 +679,6 @@ ngx_http_zstd_filter_create_cstream(ngx_http_request_t *r,
 }
 
 
-static ngx_int_t
-ngx_http_zstd_accept_encoding(ngx_str_t *ae)
-{
-    u_char  *p;
-
-    p = ngx_strcasestrn(ae->data, "zstd", sizeof("zstd") - 2);
-    if (p == NULL) {
-        return NGX_DECLINED;
-    }
-
-    if (p == ae->data || (*(p - 1) == ',' || *(p - 1) == ' ')) {
-
-        p += sizeof("zstd") - 1;
-
-        if (p == ae->data + ae->len || *p == ',' || *p == ' ' || *p == ';') {
-            return NGX_OK;
-        }
-    }
-
-    return NGX_DECLINED;
-}
-
-
-static ngx_int_t
-ngx_http_zstd_ok(ngx_http_request_t *r)
-{
-    ngx_table_elt_t  *ae;
-
-    if (r != r->main) {
-        return NGX_DECLINED;
-    }
-
-    ae = r->headers_in.accept_encoding;
-    if (ae == NULL) {
-        return NGX_DECLINED;
-    }
-
-    if (ae->value.len < sizeof("zstd") - 1) {
-        return NGX_DECLINED;
-    }
-
-    if (ngx_memcmp(ae->value.data, "zstd", 4) != 0
-        && ngx_http_zstd_accept_encoding(&ae->value) != NGX_OK)
-    {
-        return NGX_DECLINED;
-    }
-
-
-    r->gzip_tested = 1;
-    r->gzip_ok = 0;
-
-    return NGX_OK;
-}
-
-
 static void *
 ngx_http_zstd_create_main_conf(ngx_conf_t *cf)
 {
@@ -910,7 +880,6 @@ ngx_http_zstd_filter_alloc(void *opaque, size_t size)
     return p;
 }
 
-
 static ngx_int_t
 ngx_http_zstd_add_variables(ngx_conf_t *cf)
 {
diff --git a/static/config b/static/config
index ed6e66e..d85be28 100644
--- a/static/config
+++ b/static/config
@@ -100,7 +100,7 @@ CFLAGS="$ngx_zstd_opt_I $CFLAGS"
 NGX_LD_OPT="$ngx_zstd_opt_L $NGX_LD_OPT"
 
 # build the ngx_http_zstd_static_module
-HTTP_ZSTD_SRCS="$ngx_addon_dir/static/ngx_http_zstd_static_module.c"
+HTTP_ZSTD_SRCS="$ngx_addon_dir/common/ngx_http_zstd_common.c $ngx_addon_dir/static/ngx_http_zstd_static_module.c"
 
 ngx_addon_name=ngx_http_zstd_static_module
 ngx_module_type=HTTP
diff --git a/static/ngx_http_zstd_static_module.c b/static/ngx_http_zstd_static_module.c
index 3b247e9..1bd83a2 100644
--- a/static/ngx_http_zstd_static_module.c
+++ b/static/ngx_http_zstd_static_module.c
@@ -8,6 +8,8 @@
 #include <ngx_core.h>
 #include <ngx_http.h>
 
+#include "../common/ngx_http_zstd_common.h"
+
 
 #define NGX_HTTP_ZSTD_STATIC_OFF        0
 #define NGX_HTTP_ZSTD_STATIC_ON         1
@@ -40,8 +42,6 @@ static ngx_command_t  ngx_http_zstd_static_commands[] = {
 
 
 static ngx_int_t ngx_http_zstd_static_handler(ngx_http_request_t *r);
-static ngx_int_t ngx_http_zstd_accept_encoding(ngx_str_t *ae);
-static ngx_int_t ngx_http_zstd_ok(ngx_http_request_t *r);
 static void * ngx_http_zstd_static_create_loc_conf(ngx_conf_t *cf);
 static char * ngx_http_zstd_static_merge_loc_conf(ngx_conf_t *cf, void *parent,
     void *child);
@@ -78,7 +78,6 @@ ngx_module_t  ngx_http_zstd_static_module = {
     NGX_MODULE_V1_PADDING
 };
 
-
 static ngx_int_t
 ngx_http_zstd_static_handler(ngx_http_request_t *r)
 {
@@ -110,7 +109,7 @@ ngx_http_zstd_static_handler(ngx_http_request_t *r)
     }
 
     if (zscf->enable == NGX_HTTP_ZSTD_STATIC_ON) {
-        rc = ngx_http_zstd_ok(r);
+        rc = ngx_http_zstd_check_request(r);
 
     } else {
         rc = NGX_OK;
@@ -241,6 +240,9 @@ ngx_http_zstd_static_handler(ngx_http_request_t *r)
     }
 
     h->hash = 1;
+#if nginx_version >= 1023000
+    h->next = NULL;
+#endif
     ngx_str_set(&h->key, "Content-Encoding");
     ngx_str_set(&h->value, "zstd");
     r->headers_out.content_encoding = h;
@@ -280,61 +282,6 @@ ngx_http_zstd_static_handler(ngx_http_request_t *r)
 }
 
 
-static ngx_int_t
-ngx_http_zstd_ok(ngx_http_request_t *r)
-{
-    ngx_table_elt_t  *ae;
-
-    if (r != r->main) {
-        return NGX_DECLINED;
-    }
-
-    ae = r->headers_in.accept_encoding;
-    if (ae == NULL) {
-        return NGX_DECLINED;
-    }
-
-    if (ae->value.len < sizeof("zstd") - 1) {
-        return NGX_DECLINED;
-    }
-
-    if (ngx_memcmp(ae->value.data, "zstd", 4) != 0
-        && ngx_http_zstd_accept_encoding(&ae->value) != NGX_OK)
-    {
-        return NGX_DECLINED;
-    }
-
-
-    r->gzip_tested = 1;
-    r->gzip_ok = 0;
-
-    return NGX_OK;
-}
-
-
-static ngx_int_t
-ngx_http_zstd_accept_encoding(ngx_str_t *ae)
-{
-    u_char  *p;
-
-    p = ngx_strcasestrn(ae->data, "zstd", sizeof("zstd") - 1);
-    if (p == NULL) {
-        return NGX_DECLINED;
-    }
-
-    if (p == ae->data || (*(p - 1) == ',' || *(p - 1) == ' ')) {
-
-        p += sizeof("zstd") - 1;
-
-        if (p == ae->data + ae->len || *p == ',' || *p == ' ' || *p == ';') {
-            return NGX_OK;
-        }
-    }
-
-    return NGX_DECLINED;
-}
-
-
 static void *
 ngx_http_zstd_static_create_loc_conf(ngx_conf_t *cf)
 {