diff --git a/docs/libcurl/libcurl-errors.3 b/docs/libcurl/libcurl-errors.3
index c3c854e90..beabf98f0 100644
--- a/docs/libcurl/libcurl-errors.3
+++ b/docs/libcurl/libcurl-errors.3
@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2010, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -44,9 +44,15 @@ can be a misspelled protocol string or just a protocol libcurl has no code
 for.
 .IP "CURLE_FAILED_INIT (2)"
 Very early initialization code failed. This is likely to be an internal error
-or problem.
+or problem, or a resource problem where something fundamental couldn't get
+done at init time.
 .IP "CURLE_URL_MALFORMAT (3)"
 The URL was not properly formatted.
+.IP "CURLE_NOT_BUILT_IN (4)"
+A requested feature, protocol or option was not found built-in in this libcurl
+due to a build-time decision. This means that a feature or option was not
+enabled or explicitly disabled when libcurl was built and in order to get it
+to function you have to get a rebuilt libcurl.
 .IP "CURLE_COULDNT_RESOLVE_PROXY (5)"
 Couldn't resolve proxy. The given proxy host could not be resolved.
 .IP "CURLE_COULDNT_RESOLVE_HOST (6)"
@@ -145,9 +151,11 @@ CURLOPT_INTERFACE.
 .IP "CURLE_TOO_MANY_REDIRECTS (47)"
 Too many redirects. When following redirects, libcurl hit the maximum amount.
 Set your limit with CURLOPT_MAXREDIRS.
-.IP "CURLE_UNKNOWN_TELNET_OPTION (48)"
-An option set with CURLOPT_TELNETOPTIONS was not recognized/known. Refer to
-the appropriate documentation.
+.IP "CURLE_UNKNOWN_OPTION (48)"
+An option passed to libcurl is not recognized/known. Refer to the appropriate
+documentation. This is most likely a problem in the program that uses
+libcurl. The error buffer might contain more specific information about which
+exact option it concerns.
 .IP "CURLE_TELNET_OPTION_SYNTAX (49)"
 A telnet option string was Illegally formatted.
 .IP "CURLE_PEER_FAILED_VERIFICATION (51)"
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index fca917a97..aa86b913a 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -82,6 +82,7 @@ CURLE_LDAP_SEARCH_FAILED        7.1
 CURLE_LIBRARY_NOT_FOUND         7.1           7.17.0
 CURLE_LOGIN_DENIED              7.13.1
 CURLE_MALFORMAT_USER            7.1           7.17.0
+CURLE_NOT_BUILT_IN              7.21.5
 CURLE_OK                        7.1
 CURLE_OPERATION_TIMEDOUT        7.10.2
 CURLE_OPERATION_TIMEOUTED       7.1           7.17.0
@@ -123,6 +124,7 @@ CURLE_TFTP_NOTFOUND             7.15.0
 CURLE_TFTP_PERM                 7.15.0
 CURLE_TFTP_UNKNOWNID            7.15.0
 CURLE_TOO_MANY_REDIRECTS        7.5
+CURLE_UNKNOWN_OPTION            7.21.5
 CURLE_UNKNOWN_TELNET_OPTION     7.7
 CURLE_UNSUPPORTED_PROTOCOL      7.1
 CURLE_UPLOAD_FAILED             7.16.3
diff --git a/include/curl/curl.h b/include/curl/curl.h
index 73713dd07..2bd9cd042 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2010, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -401,7 +401,8 @@ typedef enum {
   CURLE_UNSUPPORTED_PROTOCOL,    /* 1 */
   CURLE_FAILED_INIT,             /* 2 */
   CURLE_URL_MALFORMAT,           /* 3 */
-  CURLE_OBSOLETE4,               /* 4 - NOT USED */
+  CURLE_NOT_BUILT_IN,            /* 4 - [was obsoleted in August 2007 for
+                                    7.17.0, reused in April 2011 for 7.21.5] */
   CURLE_COULDNT_RESOLVE_PROXY,   /* 5 */
   CURLE_COULDNT_RESOLVE_HOST,    /* 6 */
   CURLE_COULDNT_CONNECT,         /* 7 */
@@ -451,7 +452,7 @@ typedef enum {
   CURLE_INTERFACE_FAILED,        /* 45 - CURLOPT_INTERFACE failed */
   CURLE_OBSOLETE46,              /* 46 - NOT USED */
   CURLE_TOO_MANY_REDIRECTS ,     /* 47 - catch endless re-direct loops */
-  CURLE_UNKNOWN_TELNET_OPTION,   /* 48 - User specified an unknown option */
+  CURLE_UNKNOWN_OPTION,          /* 48 - User specified an unknown option */
   CURLE_TELNET_OPTION_SYNTAX ,   /* 49 - Malformed telnet option */
   CURLE_OBSOLETE50,              /* 50 - NOT USED */
   CURLE_PEER_FAILED_VERIFICATION, /* 51 - peer's certificate or fingerprint
@@ -518,6 +519,9 @@ typedef enum {
 
 /* Backwards compatibility with older names */
 
+/* The following were added in 7.21.5, April 2011 */
+#define CURLE_UNKNOWN_TELNET_OPTION CURLE_UNKNOWN_OPTION
+
 /* The following were added in 7.17.1 */
 /* These are scheduled to disappear by 2009 */
 #define CURLE_SSL_PEER_CERTIFICATE CURLE_PEER_FAILED_VERIFICATION
diff --git a/lib/axtls.h b/lib/axtls.h
index f1e94b65c..967f90930 100644
--- a/lib/axtls.h
+++ b/lib/axtls.h
@@ -51,8 +51,8 @@ int Curl_axtls_check_cxn(struct connectdata *conn);
 #define curlssl_close_all Curl_axtls_close_all
 #define curlssl_close Curl_axtls_close
 #define curlssl_shutdown(x,y) Curl_axtls_shutdown(x,y)
-#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_FAILED_INIT)
-#define curlssl_set_engine_default(x) (x=x, CURLE_FAILED_INIT)
+#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_NOT_BUILT_IN)
+#define curlssl_set_engine_default(x) (x=x, CURLE_NOT_BUILT_IN)
 #define curlssl_engines_list(x) (x=x, (struct curl_slist *)NULL)
 #define curlssl_version Curl_axtls_version
 #define curlssl_check_cxn(x) Curl_axtls_check_cxn(x)
diff --git a/lib/cyassl.h b/lib/cyassl.h
index 6dbf70f4d..a21592a28 100644
--- a/lib/cyassl.h
+++ b/lib/cyassl.h
@@ -51,9 +51,9 @@ CURLcode Curl_cyassl_connect_nonblocking(struct connectdata *conn,
 #define curlssl_session_free(x)  Curl_cyassl_session_free(x)
 #define curlssl_close_all Curl_cyassl_close_all
 #define curlssl_close Curl_cyassl_close
-#define curlssl_shutdown(x,y) Curl_cyassl_shutdown(x,y) 
-#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_FAILED_INIT)
-#define curlssl_set_engine_default(x) (x=x, CURLE_FAILED_INIT)
+#define curlssl_shutdown(x,y) Curl_cyassl_shutdown(x,y)
+#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_NOT_BUILT_IN)
+#define curlssl_set_engine_default(x) (x=x, CURLE_NOT_BUILT_IN)
 #define curlssl_engines_list(x) (x=x, (struct curl_slist *)NULL)
 #define curlssl_version Curl_cyassl_version
 #define curlssl_check_cxn(x) (x=x, -1)
diff --git a/lib/ftp.c b/lib/ftp.c
index 6a6a6de69..154a03607 100644
--- a/lib/ftp.c
+++ b/lib/ftp.c
@@ -2456,7 +2456,7 @@ static CURLcode ftp_statemach_act(struct connectdata *conn)
         default:
           failf(data, "unsupported parameter to CURLOPT_FTPSSLAUTH: %d",
                 (int)data->set.ftpsslauth);
-          return CURLE_FAILED_INIT; /* we don't know what to do */
+          return CURLE_UNKNOWN_OPTION; /* we don't know what to do */
         }
         PPSENDF(&ftpc->pp, "AUTH %s", ftpauth[ftpc->count1]);
         state(conn, FTP_AUTH);
diff --git a/lib/gtls.h b/lib/gtls.h
index 51e0af1f5..6275b49a3 100644
--- a/lib/gtls.h
+++ b/lib/gtls.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2010, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -52,8 +52,8 @@ int Curl_gtls_seed(struct SessionHandle *data);
 #define curlssl_close_all Curl_gtls_close_all
 #define curlssl_close Curl_gtls_close
 #define curlssl_shutdown(x,y) Curl_gtls_shutdown(x,y)
-#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_FAILED_INIT)
-#define curlssl_set_engine_default(x) (x=x, CURLE_FAILED_INIT)
+#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_NOT_BUILT_IN)
+#define curlssl_set_engine_default(x) (x=x, CURLE_NOT_BUILT_IN)
 #define curlssl_engines_list(x) (x=x, (struct curl_slist *)NULL)
 #define curlssl_version Curl_gtls_version
 #define curlssl_check_cxn(x) (x=x, -1)
diff --git a/lib/http_proxy.h b/lib/http_proxy.h
index da08fa50a..271b98a6e 100644
--- a/lib/http_proxy.h
+++ b/lib/http_proxy.h
@@ -29,5 +29,5 @@ CURLcode Curl_proxyCONNECT(struct connectdata *conn,
 #define PROXY_TIMEOUT (3600*1000)
 
 #else
-#define Curl_proxyCONNECT(x,y,x,w) CURLE_FAILED_INIT
+#define Curl_proxyCONNECT(x,y,x,w) CURLE_NOT_BUILT_IN
 #endif
diff --git a/lib/nssg.h b/lib/nssg.h
index f9cc46ae2..438d5a636 100644
--- a/lib/nssg.h
+++ b/lib/nssg.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2010, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -60,8 +60,8 @@ CURLcode Curl_nss_force_init(struct SessionHandle *data);
 #define curlssl_close Curl_nss_close
 /* NSS has no shutdown function provided and thus always fail */
 #define curlssl_shutdown(x,y) (x=x, y=y, 1)
-#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_FAILED_INIT)
-#define curlssl_set_engine_default(x) (x=x, CURLE_FAILED_INIT)
+#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_NOT_BUILT_IN)
+#define curlssl_set_engine_default(x) (x=x, CURLE_NOT_BUILT_IN)
 #define curlssl_engines_list(x) (x=x, (struct curl_slist *)NULL)
 #define curlssl_version Curl_nss_version
 #define curlssl_check_cxn(x) Curl_nss_check_cxn(x)
diff --git a/lib/polarssl.h b/lib/polarssl.h
index 964af1728..9e983aac9 100644
--- a/lib/polarssl.h
+++ b/lib/polarssl.h
@@ -46,8 +46,8 @@ int Curl_polarssl_shutdown(struct connectdata *conn, int sockindex);
 #define curlssl_close_all Curl_polarssl_close_all
 #define curlssl_close Curl_polarssl_close
 #define curlssl_shutdown(x,y) 0
-#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_FAILED_INIT)
-#define curlssl_set_engine_default(x) (x=x, CURLE_FAILED_INIT)
+#define curlssl_set_engine(x,y) (x=x, y=y, CURLE_NOT_BUILT_IN)
+#define curlssl_set_engine_default(x) (x=x, CURLE_NOT_BUILT_IN)
 #define curlssl_engines_list(x) (x=x, (struct curl_slist *)NULL)
 #define curlssl_version Curl_polarssl_version
 #define curlssl_check_cxn(x) (x=x, -1)
diff --git a/lib/qssl.h b/lib/qssl.h
index 45190e623..bd195ff7b 100644
--- a/lib/qssl.h
+++ b/lib/qssl.h
@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2008, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -49,8 +49,8 @@ int Curl_qsossl_check_cxn(struct connectdata * cxn);
 #define curlssl_close_all Curl_qsossl_close_all
 #define curlssl_close Curl_qsossl_close
 #define curlssl_shutdown(x,y) Curl_qsossl_shutdown(x,y)
-#define curlssl_set_engine(x,y) CURLE_FAILED_INIT
-#define curlssl_set_engine_default(x) CURLE_FAILED_INIT
+#define curlssl_set_engine(x,y) CURLE_NOT_BUILT_IN
+#define curlssl_set_engine_default(x) CURLE_NOT_BUILT_IN
 #define curlssl_engines_list(x) NULL
 #define curlssl_version Curl_qsossl_version
 #define curlssl_check_cxn(x) Curl_qsossl_check_cxn(x)
diff --git a/lib/socks.h b/lib/socks.h
index 1c686d181..42b8080b0 100644
--- a/lib/socks.h
+++ b/lib/socks.h
@@ -25,8 +25,8 @@
 #include "setup.h"
 
 #ifdef CURL_DISABLE_PROXY
-#define Curl_SOCKS4(a,b,c,d,e,f) CURLE_FAILED_INIT
-#define Curl_SOCKS5(a,b,c,d,e,f) CURLE_FAILED_INIT
+#define Curl_SOCKS4(a,b,c,d,e,f) CURLE_NOT_BUILT_IN
+#define Curl_SOCKS5(a,b,c,d,e,f) CURLE_NOT_BUILT_IN
 #else
 /*
  * Helper read-from-socket functions. Does the same as Curl_read() but it
diff --git a/lib/sslgen.h b/lib/sslgen.h
index af582e06f..b0a0fab12 100644
--- a/lib/sslgen.h
+++ b/lib/sslgen.h
@@ -72,12 +72,12 @@ void Curl_ssl_delsessionid(struct connectdata *conn, void *ssl_sessionid);
 /* When SSL support is not present, just define away these function calls */
 #define Curl_ssl_init() 1
 #define Curl_ssl_cleanup() do { } while (0)
-#define Curl_ssl_connect(x,y) CURLE_FAILED_INIT
+#define Curl_ssl_connect(x,y) CURLE_NOT_BUILT_IN
 #define Curl_ssl_close_all(x)
 #define Curl_ssl_close(x,y)
-#define Curl_ssl_shutdown(x,y) CURLE_FAILED_INIT
-#define Curl_ssl_set_engine(x,y) CURLE_FAILED_INIT
-#define Curl_ssl_set_engine_default(x) CURLE_FAILED_INIT
+#define Curl_ssl_shutdown(x,y) CURLE_NOT_BUILT_IN
+#define Curl_ssl_set_engine(x,y) CURLE_NOT_BUILT_IN
+#define Curl_ssl_set_engine_default(x) CURLE_NOT_BUILT_IN
 #define Curl_ssl_engines_list(x) NULL
 #define Curl_ssl_send(a,b,c,d,e) -1
 #define Curl_ssl_recv(a,b,c,d,e) -1
@@ -86,7 +86,7 @@ void Curl_ssl_delsessionid(struct connectdata *conn, void *ssl_sessionid);
 #define Curl_ssl_data_pending(x,y) 0
 #define Curl_ssl_check_cxn(x) 0
 #define Curl_ssl_free_certinfo(x)
-#define Curl_ssl_connect_nonblocking(x,y,z) CURLE_FAILED_INIT
+#define Curl_ssl_connect_nonblocking(x,y,z) CURLE_NOT_BUILT_IN
 #endif
 
 #endif /* USE_SSL */
diff --git a/lib/strerror.c b/lib/strerror.c
index a88cdc4eb..8144f78f0 100644
--- a/lib/strerror.c
+++ b/lib/strerror.c
@@ -65,6 +65,10 @@ curl_easy_strerror(CURLcode error)
   case CURLE_URL_MALFORMAT:
     return "URL using bad/illegal format or missing URL";
 
+  case CURLE_NOT_BUILT_IN:
+    return "A requested feature, protocol or option was not found built-in in"
+      " this libcurl due to a build-time decision.";
+
   case CURLE_COULDNT_RESOLVE_PROXY:
     return "Couldn't resolve proxy name";
 
@@ -167,8 +171,8 @@ curl_easy_strerror(CURLcode error)
   case CURLE_TOO_MANY_REDIRECTS :
     return "Number of redirects hit maximum amount";
 
-  case CURLE_UNKNOWN_TELNET_OPTION:
-    return "User specified an unknown telnet option";
+  case CURLE_UNKNOWN_OPTION:
+    return "An unknown option was passed in to libcurl";
 
   case CURLE_TELNET_OPTION_SYNTAX :
     return "Malformed telnet option";
@@ -282,7 +286,6 @@ curl_easy_strerror(CURLcode error)
     return "Chunk callback failed";
 
     /* error codes not used by current libcurl */
-  case CURLE_OBSOLETE4:
   case CURLE_OBSOLETE10:
   case CURLE_OBSOLETE12:
   case CURLE_OBSOLETE16:
diff --git a/lib/url.c b/lib/url.c
index 5ece35ed2..c7fcdfe96 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -988,7 +988,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
       break;
     default:
       /* reserve other values for future use */
-      result = CURLE_FAILED_INIT;
+      result = CURLE_UNKNOWN_OPTION;
       break;
     }
     break;
@@ -1428,7 +1428,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     auth &= ~CURLAUTH_GSSNEGOTIATE; /* no GSS-Negotiate without GSSAPI or WINDOWS_SSPI */
 #endif
     if(!auth)
-      return CURLE_FAILED_INIT; /* no supported types left! */
+      return CURLE_NOT_BUILT_IN; /* no supported types left! */
 
     data->set.httpauth = auth;
   }
@@ -1488,7 +1488,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     auth &= ~CURLAUTH_GSSNEGOTIATE; /* no GSS-Negotiate without GSSAPI or WINDOWS_SSPI */
 #endif
     if(!auth)
-      return CURLE_FAILED_INIT; /* no supported types left! */
+      return CURLE_NOT_BUILT_IN; /* no supported types left! */
 
     data->set.proxyauth = auth;
   }
@@ -1528,7 +1528,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
       break;
     default:
       /* reserve other values for future use */
-      result = CURLE_FAILED_INIT;
+      result = CURLE_UNKNOWN_OPTION;
       break;
     }
     break;
@@ -2518,7 +2518,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
 #endif
   default:
     /* unknown tag and its companion, just ignore: */
-    result = CURLE_FAILED_INIT; /* correct this */
+    result = CURLE_UNKNOWN_OPTION;
     break;
   }