Index: subversion/mod_dav_svn/util.c
===================================================================
--- subversion/mod_dav_svn/util.c	(revision 999170)
+++ subversion/mod_dav_svn/util.c	(working copy)
@@ -107,6 +107,9 @@ dav_svn__convert_err(svn_error_t *serr,
       case SVN_ERR_FS_PATH_ALREADY_LOCKED:
         status = HTTP_LOCKED;
         break;
+      case SVN_ERR_FS_PROP_BASEVALUE_MISMATCH:
+        status = HTTP_PRECONDITION_FAILED;
+        break;
         /* add other mappings here */
       }
 
Index: subversion/libsvn_ra_neon/util.c
===================================================================
--- subversion/libsvn_ra_neon/util.c	(revision 999170)
+++ subversion/libsvn_ra_neon/util.c	(working copy)
@@ -167,6 +167,7 @@ typedef struct
   svn_ra_neon__request_t *req;
   svn_stringbuf_t *description;
   svn_boolean_t contains_error;
+  svn_boolean_t contains_precondition_error;
 } multistatus_baton_t;
 
 /* Implements svn_ra_neon__startelm_cb_t. */
@@ -231,6 +232,9 @@ end_207_element(void *baton, int state,
             return svn_error_create(SVN_ERR_RA_DAV_REQUEST_FAILED, NULL,
                                     _("The request response contained at least "
                                       "one error"));
+          else if (b->contains_precondition_error) 
+            return svn_error_create(SVN_ERR_FS_PROP_BASEVALUE_MISMATCH, NULL,
+                                    b->description->data);
           else
             return svn_error_create(SVN_ERR_RA_DAV_REQUEST_FAILED, NULL,
                                     b->description->data);
@@ -260,6 +264,10 @@ end_207_element(void *baton, int state,
             else
               b->propstat_has_error = (status.klass != 2);
 
+            /* Handle "412 Precondition Failed" specially */
+            if (status.code == 412)
+              b->contains_precondition_error = TRUE;
+
             free(status.reason_phrase);
           }
         else
Index: subversion/libsvn_ra_serf/util.c
===================================================================
--- subversion/libsvn_ra_serf/util.c	(revision 999170)
+++ subversion/libsvn_ra_serf/util.c	(working copy)
@@ -836,6 +836,7 @@ svn_ra_serf__handle_discard_body(serf_request_t *r
             {
               server_err->error = svn_error_create(APR_SUCCESS, NULL, NULL);
               server_err->has_xml_response = TRUE;
+              server_err->contains_precondition_error = FALSE;
               server_err->cdata = svn_stringbuf_create("", pool);
               server_err->collect_cdata = FALSE;
               server_err->parser.pool = server_err->error->pool;
@@ -945,6 +946,34 @@ svn_ra_serf__handle_status_only(serf_request_t *re
   return svn_error_return(err);
 }
 
+/* Given a string like "HTTP/1.1 500 (status)" in BUF, parse out the numeric
+   status code into *STATUS_CODE_OUT.  Ignores leading whitespace. */
+static svn_error_t *
+parse_dav_status(int *status_code_out, svn_stringbuf_t *buf,
+                 apr_pool_t *scratch_pool)
+{
+  svn_error_t *err;
+  const char *token;
+  char *tok_status;
+  svn_stringbuf_t *temp_buf = svn_stringbuf_dup(buf, scratch_pool);
+
+  svn_stringbuf_strip_whitespace(temp_buf);
+  token = apr_strtok(temp_buf->data, " \t\r\n", &tok_status);
+  if (token)
+    token = apr_strtok(NULL, " \t\r\n", &tok_status);
+  if (!token)
+    return svn_error_createf(SVN_ERR_RA_DAV_MALFORMED_DATA, NULL,
+                             "Malformed DAV:status CDATA '%s'",
+                             buf->data);
+  err = svn_cstring_atoi(status_code_out, token);
+  if (err)
+    return svn_error_createf(SVN_ERR_RA_DAV_MALFORMED_DATA, err,
+                             "Malformed DAV:status CDATA '%s'",
+                             buf->data);
+
+  return SVN_NO_ERROR;
+}
+
 /*
  * Expat callback invoked on a start element tag for a 207 response.
  */
@@ -968,6 +997,14 @@ start_207(svn_ra_serf__xml_parser_t *parser,
       svn_stringbuf_setempty(ctx->cdata);
       ctx->collect_cdata = TRUE;
     }
+  else if (ctx->in_error &&
+           strcmp(name.namespace, "DAV:") == 0 &&
+           strcmp(name.name, "status") == 0)
+    {
+      /* Start collecting cdata. */
+      svn_stringbuf_setempty(ctx->cdata);
+      ctx->collect_cdata = TRUE;
+    }
 
   return SVN_NO_ERROR;
 }
@@ -993,9 +1030,24 @@ end_207(svn_ra_serf__xml_parser_t *parser,
       ctx->collect_cdata = FALSE;
       ctx->error->message = apr_pstrmemdup(ctx->error->pool, ctx->cdata->data,
                                            ctx->cdata->len);
-      ctx->error->apr_err = SVN_ERR_RA_DAV_REQUEST_FAILED;
+      if (ctx->contains_precondition_error)
+        ctx->error->apr_err = SVN_ERR_FS_PROP_BASEVALUE_MISMATCH;
+      else
+        ctx->error->apr_err = SVN_ERR_RA_DAV_REQUEST_FAILED;
     }
+  else if (ctx->in_error &&
+           strcmp(name.namespace, "DAV:") == 0 &&
+           strcmp(name.name, "status") == 0)
+    {
+      int status_code;
 
+      ctx->collect_cdata = FALSE;
+
+      SVN_ERR(parse_dav_status(&status_code, ctx->cdata, parser->pool));
+      if (status_code == 412)
+        ctx->contains_precondition_error = TRUE;
+    }
+
   return SVN_NO_ERROR;
 }
 
@@ -1044,6 +1096,7 @@ svn_ra_serf__handle_multistatus_only(serf_request_
         {
           server_err->error = svn_error_create(APR_SUCCESS, NULL, NULL);
           server_err->has_xml_response = TRUE;
+          server_err->contains_precondition_error = FALSE;
           server_err->cdata = svn_stringbuf_create("", pool);
           server_err->collect_cdata = FALSE;
           server_err->parser.pool = server_err->error->pool;
Index: subversion/libsvn_ra_serf/ra_serf.h
===================================================================
--- subversion/libsvn_ra_serf/ra_serf.h	(revision 999170)
+++ subversion/libsvn_ra_serf/ra_serf.h	(working copy)
@@ -673,6 +673,9 @@ typedef struct svn_ra_serf__server_error_t {
   /* Have we seen an error tag? */
   svn_boolean_t in_error;
 
+  /* Have we seen a HTTP "412 Precondition Failed" error? */
+  svn_boolean_t contains_precondition_error;
+
   /* Should we be collecting the XML cdata? */
   svn_boolean_t collect_cdata;