diff --git a/docs/cmdline-opts/page-footer b/docs/cmdline-opts/page-footer
index 613a3e8de1..1e2efe5cbb 100644
--- a/docs/cmdline-opts/page-footer
+++ b/docs/cmdline-opts/page-footer
@@ -217,8 +217,6 @@ option to curl that was passed on to libcurl and rejected. Read up in the
 manual!
 .IP 49
 Malformed telnet option.
-.IP 51
-The peer's SSL certificate or SSH MD5 fingerprint was not OK.
 .IP 52
 The server did not reply anything, which here is considered an error.
 .IP 53
@@ -237,8 +235,6 @@ Could not use specified SSL cipher.
 Peer certificate cannot be authenticated with known CA certificates.
 .IP 61
 Unrecognized transfer encoding.
-.IP 62
-Invalid LDAP URL.
 .IP 63
 Maximum file size exceeded.
 .IP 64
@@ -263,10 +259,6 @@ Unknown TFTP transfer ID.
 File already exists (TFTP).
 .IP 74
 No such user (TFTP).
-.IP 75
-Character conversion failed.
-.IP 76
-Character conversion functions required.
 .IP 77
 Problem reading the SSL CA cert (path? access rights?).
 .IP 78
diff --git a/docs/libcurl/libcurl-errors.3 b/docs/libcurl/libcurl-errors.3
index c5a8663768..78d5101d47 100644
--- a/docs/libcurl/libcurl-errors.3
+++ b/docs/libcurl/libcurl-errors.3
@@ -96,6 +96,8 @@ does not match the previously given size.
 .IP "CURLE_FTP_COULDNT_RETR_FILE (19)"
 This was either a weird reply to a 'RETR' command or a zero byte transfer
 complete.
+.IP "Obsolete error (20)"
+Not used in modern versions.
 .IP "CURLE_QUOTE_ERROR (21)"
 When sending custom "QUOTE" commands to the remote server, one of the commands
 returned an error code that was 400 or higher (for FTP) or otherwise
@@ -106,6 +108,8 @@ server returns an error code that is >= 400.
 .IP "CURLE_WRITE_ERROR (23)"
 An error occurred when writing received data to a local file, or an error was
 returned to libcurl from a write callback.
+.IP "Obsolete error (24)"
+Not used in modern versions.
 .IP "CURLE_UPLOAD_FAILED (25)"
 Failed starting the upload. For FTP, the server typically denied the STOR
 command. The error buffer usually contains the server's explanation for this.
@@ -118,6 +122,8 @@ things are severely screwed up if this ever occurs.
 .IP "CURLE_OPERATION_TIMEDOUT (28)"
 Operation timeout. The specified time-out period was reached according to the
 conditions.
+.IP "Obsolete error (29)"
+Not used in modern versions.
 .IP "CURLE_FTP_PORT_FAILED (30)"
 The FTP PORT command returned error. This mostly happens when you have not
 specified a good enough address for libcurl to use. See
@@ -125,6 +131,8 @@ specified a good enough address for libcurl to use. See
 .IP "CURLE_FTP_COULDNT_USE_REST (31)"
 The FTP REST command returned error. This should never happen if the server is
 sane.
+.IP "Obsolete error (32)"
+Not used in modern versions.
 .IP "CURLE_RANGE_ERROR (33)"
 The server does not support or accept range requests.
 .IP "CURLE_HTTP_POST_ERROR (34)"
@@ -144,16 +152,22 @@ path does not identify an existing file. Did you check file permissions?
 LDAP cannot bind. LDAP bind operation failed.
 .IP "CURLE_LDAP_SEARCH_FAILED (39)"
 LDAP search failed.
+.IP "Obsolete error (40)"
+Not used in modern versions.
 .IP "CURLE_FUNCTION_NOT_FOUND (41)"
 Function not found. A required zlib function was not found.
 .IP "CURLE_ABORTED_BY_CALLBACK (42)"
 Aborted by callback. A callback returned "abort" to libcurl.
 .IP "CURLE_BAD_FUNCTION_ARGUMENT (43)"
 A function was called with a bad parameter.
+.IP "Obsolete error (44)"
+Not used in modern versions.
 .IP "CURLE_INTERFACE_FAILED (45)"
 Interface error. A specified outgoing interface could not be used. Set which
 interface to use for outgoing connections' source IP address with
 \fICURLOPT_INTERFACE(3)\fP.
+.IP "Obsolete error (46)"
+Not used in modern versions.
 .IP "CURLE_TOO_MANY_REDIRECTS (47)"
 Too many redirects. When following redirects, libcurl hit the maximum amount.
 Set your limit with \fICURLOPT_MAXREDIRS(3)\fP.
@@ -165,6 +179,8 @@ exact option it concerns.
 .IP "CURLE_SETOPT_OPTION_SYNTAX (49)"
 An option passed in to a setopt was wrongly formatted. See error message for
 details about what option.
+.IP "Obsolete errors (50-51)"
+Not used in modern versions.
 .IP "CURLE_GOT_NOTHING (52)"
 Nothing was returned from the server, and under the circumstances, getting
 nothing is considered an error.
@@ -176,6 +192,8 @@ Failed setting the selected SSL crypto engine as default.
 Failed sending network data.
 .IP "CURLE_RECV_ERROR (56)"
 Failure with receiving network data.
+.IP "Obsolete error (57)"
+Not used in modern versions.
 .IP "CURLE_SSL_CERTPROBLEM (58)"
 problem with the local client certificate.
 .IP "CURLE_SSL_CIPHER (59)"
@@ -186,8 +204,8 @@ This error code has been unified with CURLE_SSL_CACERT since 7.62.0. Its
 previous value was 51.
 .IP "CURLE_BAD_CONTENT_ENCODING (61)"
 Unrecognized transfer encoding.
-.IP "CURLE_LDAP_INVALID_URL (62)"
-This error code is deprecated since 7.82.0 and cannot be returned anymore.
+.IP "Obsolete error (62)"
+Not used in modern versions.
 .IP "CURLE_FILESIZE_EXCEEDED (63)"
 Maximum file size exceeded.
 .IP "CURLE_USE_SSL_FAILED (64)"
@@ -213,10 +231,8 @@ Unknown TFTP transfer ID.
 File already exists and will not be overwritten.
 .IP "CURLE_TFTP_NOSUCHUSER (74)"
 This error should never be returned by a properly functioning TFTP server.
-.IP "CURLE_CONV_FAILED (75)"
-Character conversion failed.
-.IP "CURLE_CONV_REQD (76)"
-Caller must register conversion callbacks.
+.IP "Obsolete error (75-76)"
+Not used in modern versions.
 .IP "CURLE_SSL_CACERT_BADFILE (77)"
 Problem with reading the SSL CA cert (path? access rights?)
 .IP "CURLE_REMOTE_FILE_NOT_FOUND (78)"
@@ -265,6 +281,9 @@ be one out of several problems, see the error buffer for details.
 .IP "CURLE_QUIC_CONNECT_ERROR (96)"
 QUIC connection error. This error may be caused by an SSL library error. QUIC
 is the protocol used for HTTP/3 transfers.
+.IP "CURLE_PROXY (97)"
+Proxy handshake error. \fICURLINFO_PROXY_ERROR(3)\fP provides extra details on
+the specific problem.
 .IP "CURLE_SSL_CLIENTCERT (98)"
 SSL Client Certificate required.
 .IP "CURLE_UNRECOVERABLE_POLL (99)"
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index c590d084f1..74e2418540 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -217,7 +217,7 @@ CURLE_BAD_DOWNLOAD_RESUME       7.10
 CURLE_BAD_FUNCTION_ARGUMENT     7.1
 CURLE_BAD_PASSWORD_ENTERED      7.4.2         7.17.0
 CURLE_CHUNK_FAILED              7.21.0
-CURLE_CONV_FAILED               7.15.4
+CURLE_CONV_FAILED               7.15.4        7.82.0
 CURLE_CONV_REQD                 7.15.4        7.82.0
 CURLE_COULDNT_CONNECT           7.1
 CURLE_COULDNT_RESOLVE_HOST      7.1
diff --git a/include/curl/curl.h b/include/curl/curl.h
index b00648e791..6527f2149e 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -577,7 +577,7 @@ typedef enum {
   CURLE_TFTP_UNKNOWNID,          /* 72 - Unknown transfer ID */
   CURLE_REMOTE_FILE_EXISTS,      /* 73 - File already exists */
   CURLE_TFTP_NOSUCHUSER,         /* 74 - No such user */
-  CURLE_CONV_FAILED,             /* 75 - conversion failed */
+  CURLE_OBSOLETE75,              /* 75 - NOT IN USE since 7.82.0 */
   CURLE_OBSOLETE76,              /* 76 - NOT IN USE since 7.82.0 */
   CURLE_SSL_CACERT_BADFILE,      /* 77 - could not load CACERT file, missing
                                     or wrong format */
@@ -680,6 +680,7 @@ typedef enum {
 #define CURLE_FTP_BAD_DOWNLOAD_RESUME CURLE_BAD_DOWNLOAD_RESUME
 #define CURLE_LDAP_INVALID_URL CURLE_OBSOLETE62
 #define CURLE_CONV_REQD CURLE_OBSOLETE76
+#define CURLE_CONV_FAILED CURLE_OBSOLETE75
 
 /* This was the error code 50 in 7.7.3 and a few earlier versions, this
    is no longer used by libcurl but is instead #defined here only to not
diff --git a/lib/strerror.c b/lib/strerror.c
index be43fd6c84..eceb1668a1 100644
--- a/lib/strerror.c
+++ b/lib/strerror.c
@@ -265,9 +265,6 @@ curl_easy_strerror(CURLcode error)
   case CURLE_TFTP_NOSUCHUSER:
     return "TFTP: No such user";
 
-  case CURLE_CONV_FAILED:
-    return "Conversion failed";
-
   case CURLE_REMOTE_FILE_NOT_FOUND:
     return "Remote file not found";
 
@@ -334,6 +331,7 @@ curl_easy_strerror(CURLcode error)
   case CURLE_OBSOLETE51:
   case CURLE_OBSOLETE57:
   case CURLE_OBSOLETE62:
+  case CURLE_OBSOLETE75:
   case CURLE_OBSOLETE76:
   case CURL_LAST:
     break;
diff --git a/tests/data/test1538 b/tests/data/test1538
index e21d0537f5..6df7983e6b 100644
--- a/tests/data/test1538
+++ b/tests/data/test1538
@@ -107,7 +107,7 @@ e71: TFTP: Illegal operation
 e72: TFTP: Unknown transfer ID
 e73: Remote file already exists
 e74: TFTP: No such user
-e75: Conversion failed
+e75: Unknown error
 e76: Unknown error
 e77: Problem with the SSL CA cert (path? access rights?)
 e78: Remote file not found