diff --git a/ssl/custom_extensions.c b/ssl/custom_extensions.c
index 780cdc68..46b5efb4 100644
--- a/ssl/custom_extensions.c
+++ b/ssl/custom_extensions.c
@@ -90,7 +90,7 @@ static int custom_ext_add_hello(SSL *ssl, CBB *extensions) {
             !CBB_add_bytes(&contents_cbb, contents, contents_len) ||
             !CBB_flush(extensions)) {
           OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
-          ERR_add_error_dataf("extension: %u", (unsigned) ext->value);
+          ERR_add_error_dataf("extension %u", (unsigned) ext->value);
           if (ext->free_callback && 0 < contents_len) {
             ext->free_callback(ssl, ext->value, contents, ext->add_arg);
           }
@@ -113,7 +113,7 @@ static int custom_ext_add_hello(SSL *ssl, CBB *extensions) {
       default:
         ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
         OPENSSL_PUT_ERROR(SSL, SSL_R_CUSTOM_EXTENSION_ERROR);
-        ERR_add_error_dataf("extension: %u", (unsigned) ext->value);
+        ERR_add_error_dataf("extension %u", (unsigned) ext->value);
         return 0;
     }
   }
@@ -136,7 +136,7 @@ int custom_ext_parse_serverhello(SSL *ssl, int *out_alert, uint16_t value,
       /* Also, if we didn't send the extension, that's also unacceptable. */
       !(ssl->s3->hs->custom_extensions.sent & (1u << index))) {
     OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
-    ERR_add_error_dataf("extension: %u", (unsigned)value);
+    ERR_add_error_dataf("extension %u", (unsigned)value);
     *out_alert = SSL_AD_UNSUPPORTED_EXTENSION;
     return 0;
   }
@@ -145,7 +145,7 @@ int custom_ext_parse_serverhello(SSL *ssl, int *out_alert, uint16_t value,
       !ext->parse_callback(ssl, value, CBS_data(extension), CBS_len(extension),
                            out_alert, ext->parse_arg)) {
     OPENSSL_PUT_ERROR(SSL, SSL_R_CUSTOM_EXTENSION_ERROR);
-    ERR_add_error_dataf("extension: %u", (unsigned)ext->value);
+    ERR_add_error_dataf("extension %u", (unsigned)ext->value);
     return 0;
   }
 
@@ -169,7 +169,7 @@ int custom_ext_parse_clienthello(SSL *ssl, int *out_alert, uint16_t value,
       !ext->parse_callback(ssl, value, CBS_data(extension), CBS_len(extension),
                            out_alert, ext->parse_arg)) {
     OPENSSL_PUT_ERROR(SSL, SSL_R_CUSTOM_EXTENSION_ERROR);
-    ERR_add_error_dataf("extension: %u", (unsigned)ext->value);
+    ERR_add_error_dataf("extension %u", (unsigned)ext->value);
     return 0;
   }
 
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index bc39440f..3679f8d7 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2651,7 +2651,7 @@ int ssl_add_clienthello_tlsext(SSL *ssl, CBB *out, size_t header_len) {
     const size_t len_before = CBB_len(&extensions);
     if (!kExtensions[i].add_clienthello(ssl, &extensions)) {
       OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_ADDING_EXTENSION);
-      ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
+      ERR_add_error_dataf("extension %u", (unsigned)kExtensions[i].value);
       goto err;
     }
 
@@ -2744,7 +2744,7 @@ int ssl_add_serverhello_tlsext(SSL *ssl, CBB *out) {
 
     if (!kExtensions[i].add_serverhello(ssl, &extensions)) {
       OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_ADDING_EXTENSION);
-      ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
+      ERR_add_error_dataf("extension %u", (unsigned)kExtensions[i].value);
       goto err;
     }
   }
@@ -2814,7 +2814,7 @@ static int ssl_scan_clienthello_tlsext(
     if (!ext->parse_clienthello(ssl, &alert, &extension)) {
       *out_alert = alert;
       OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_PARSING_EXTENSION);
-      ERR_add_error_dataf("extension: %u", (unsigned)type);
+      ERR_add_error_dataf("extension %u", (unsigned)type);
       return 0;
     }
   }
@@ -2842,7 +2842,7 @@ static int ssl_scan_clienthello_tlsext(
     uint8_t alert = SSL_AD_DECODE_ERROR;
     if (!kExtensions[i].parse_clienthello(ssl, &alert, contents)) {
       OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
-      ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
+      ERR_add_error_dataf("extension %u", (unsigned)kExtensions[i].value);
       *out_alert = alert;
       return 0;
     }
@@ -2921,7 +2921,7 @@ static int ssl_scan_serverhello_tlsext(SSL *ssl, CBS *cbs, int *out_alert) {
     uint8_t alert = SSL_AD_DECODE_ERROR;
     if (!ext->parse_serverhello(ssl, &alert, &extension)) {
       OPENSSL_PUT_ERROR(SSL, SSL_R_ERROR_PARSING_EXTENSION);
-      ERR_add_error_dataf("extension: %u", (unsigned)type);
+      ERR_add_error_dataf("extension %u", (unsigned)type);
       *out_alert = alert;
       return 0;
     }
@@ -2934,7 +2934,7 @@ static int ssl_scan_serverhello_tlsext(SSL *ssl, CBS *cbs, int *out_alert) {
       uint8_t alert = SSL_AD_DECODE_ERROR;
       if (!kExtensions[i].parse_serverhello(ssl, &alert, NULL)) {
         OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_EXTENSION);
-        ERR_add_error_dataf("extension: %u", (unsigned)kExtensions[i].value);
+        ERR_add_error_dataf("extension %u", (unsigned)kExtensions[i].value);
         *out_alert = alert;
         return 0;
       }