diff --git a/NEWS.md b/NEWS.md
index 8035002a8..7e7c347c2 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -20,6 +20,8 @@
 
 - Added the same CSS as in default Pandoc's template for when a CSL is used (#1045).   
 
+- No more warnings are thrown when passing several input files to `render_book(preview = TRUE)` (#1091).
+
 ## MINOR CHANGES
 
 - `anchor_sections = TRUE` becomes the default for `bookdown::gitbook()`.
diff --git a/R/render.R b/R/render.R
index c0f7c326e..afc7d1f79 100644
--- a/R/render.R
+++ b/R/render.R
@@ -113,7 +113,7 @@ render_book = function(
   # store output directory and the initial input Rmd name
   opts$set(
     output_dir = output_dir,
-    input_rmd = xfun::relative_path(input, dir = "."),
+    input_rmd = relative_path(input),
     preview = preview
   )
 
diff --git a/R/utils.R b/R/utils.R
index 485acae8f..266e34f09 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -284,6 +284,12 @@ dir_create = function(path) {
   dir_exists(path) || dir.create(path, recursive = TRUE)
 }
 
+# vectorized version to get relative path of multiple input
+relative_path = function(inputs, dir = ".") {
+  f = Vectorize(xfun::relative_path, "x", USE.NAMES = FALSE)
+  f(x = inputs, dir = dir, use.. = TRUE, error = TRUE)
+}
+
 # a wrapper of file.path to ignore `output_dir` if it is NULL
 output_path = function(...) {
   dir = opts$get('output_dir')
diff --git a/tests/testit/test-utils.R b/tests/testit/test-utils.R
index 78b71b7a1..e8e32668a 100644
--- a/tests/testit/test-utils.R
+++ b/tests/testit/test-utils.R
@@ -165,3 +165,8 @@ assert('fence_theorems() converts the knitr engine syntax to fenced Divs', {
   res = fence_theorems(text = old)
   (unclass(res) %==% old)
 })
+
+assert("relative_path is vectorized", {
+  relative_path(c('foo/bar.txt', 'foo/baz.txt'), 'foo/') %==% c("bar.txt", "baz.txt")
+  relative_path('foo/bar.txt', 'foo') %==% "bar.txt"
+})