diff --git a/NAMESPACE b/NAMESPACE
index 820a327aa..9a559a607 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -204,6 +204,7 @@ export(selectizeInput)
 export(serverInfo)
 export(setBookmarkExclude)
 export(setProgress)
+export(setSerializer)
 export(shinyApp)
 export(shinyAppDir)
 export(shinyAppFile)
diff --git a/NEWS.md b/NEWS.md
index 4a20f505e..f155fcdd6 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -31,6 +31,8 @@ shiny 1.0.3.9001
 
 * Added a function `isRunning` to test whether a Shiny app is currently running. ([#1785](https://github.com/rstudio/shiny/pull/1785))
 
+* Added a function `setSerializer`, which allows authors to specify a function for serializing the value of a custom input. ([#1791](https://github.com/rstudio/shiny/pull/1791))
+
 ### Bug fixes
 
 * Fixed [#1546](https://github.com/rstudio/shiny/issues/1546): make it possible (without any hacks) to write arbitrary data into a module's `session$userData` (which is exactly the same environment as the parent's `session$userData`). To be clear, it allows something like `session$userData$x <- TRUE`, but not something like `session$userData <- TRUE` (that is not allowed in any context, whether you're in the main app, or in a module) ([#1732](https://github.com/rstudio/shiny/pull/1732)).
diff --git a/R/serializers.R b/R/serializers.R
index 1fdb8b021..35f3b4692 100644
--- a/R/serializers.R
+++ b/R/serializers.R
@@ -1,3 +1,22 @@
+#' Add a function for serializing an input before bookmarking application state
+#'
+#' @param inputId Name of the input value.
+#' @param fun A function that takes the input value and returns a modified
+#'   value. The returned value will be used for the test snapshot.
+#' @param session A Shiny session object.
+#'
+#' @keywords internal
+#' @export
+setSerializer <- function(inputId, fun, session = getDefaultReactiveDomain()) {
+  if (is.null(session)) {
+    stop("setSerializer() needs a session object.")
+  }
+
+  input_impl <- .subset2(session$input, "impl")
+  input_impl$setMeta(inputId, "shiny.serializer", fun)
+}
+
+
 # For most types of values, simply return the value unchanged.
 serializerDefault <- function(value, stateDir) {
   value
@@ -58,12 +77,12 @@ serializeReactiveValues <- function(values, exclude, stateDir = NULL) {
 
     # Get the serializer function for this input value. If none specified, use
     # the default.
-    serializer <- impl$getMeta(name, "shiny.serializer")
-    if (is.null(serializer))
-      serializer <- serializerDefault
+    serializer_fun <- impl$getMeta(name, "shiny.serializer")
+    if (is.null(serializer_fun))
+      serializer_fun <- serializerDefault
 
     # Apply serializer function.
-    serializer(val, stateDir)
+    serializer_fun(val, stateDir)
   })
 
   # Filter out any values that were marked as unserializable.
diff --git a/R/server-input-handlers.R b/R/server-input-handlers.R
index cbdb8c475..cc602e5b2 100644
--- a/R/server-input-handlers.R
+++ b/R/server-input-handlers.R
@@ -148,7 +148,7 @@ registerInputHandler("shiny.number", function(val, ...){
 
 registerInputHandler("shiny.password", function(val, shinysession, name) {
   # Mark passwords as not serializable
-  .subset2(shinysession$input, "impl")$setMeta(name, "shiny.serializer", serializerUnserializable)
+  setSerializer(name, serializerUnserializable)
   val
 })
 
@@ -214,7 +214,7 @@ registerInputHandler("shiny.file", function(val, shinysession, name) {
   # Need to mark this input value with the correct serializer. When a file is
   # uploaded the usual way (instead of being restored), this occurs in
   # session$`@uploadEnd`.
-  .subset2(shinysession$input, "impl")$setMeta(name, "shiny.serializer", serializerFileInput)
+  setSerializer(name, serializerFileInput)
 
   snapshotPreprocessInput(name, snapshotPreprocessorFileInput)
 
diff --git a/R/shiny.R b/R/shiny.R
index 72cca31c8..872cdb2f4 100644
--- a/R/shiny.R
+++ b/R/shiny.R
@@ -1530,7 +1530,7 @@ ShinySession <- R6Class(
       fileData <- private$fileUploadContext$getUploadOperation(jobId)$finish()
       private$.input$set(inputId, fileData)
 
-      private$.input$setMeta(inputId, "shiny.serializer", serializerFileInput)
+      setSerializer(inputId, serializerFileInput)
       snapshotPreprocessInput(inputId, snapshotPreprocessorFileInput)
 
       invisible()
diff --git a/inst/staticdocs/index.r b/inst/staticdocs/index.r
index 38d8e708b..69f2981b7 100644
--- a/inst/staticdocs/index.r
+++ b/inst/staticdocs/index.r
@@ -194,6 +194,7 @@ sd_section("Utility functions",
     "parseQueryString",
     "plotPNG",
     "exportTestValues",
+    "setSerializer",
     "snapshotExclude",
     "snapshotPreprocessInput",
     "snapshotPreprocessOutput",
diff --git a/man/setSerializer.Rd b/man/setSerializer.Rd
new file mode 100644
index 000000000..ef10eba62
--- /dev/null
+++ b/man/setSerializer.Rd
@@ -0,0 +1,20 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/serializers.R
+\name{setSerializer}
+\alias{setSerializer}
+\title{Add a function for serializing an input before bookmarking application state}
+\usage{
+setSerializer(inputId, fun, session = getDefaultReactiveDomain())
+}
+\arguments{
+\item{inputId}{Name of the input value.}
+
+\item{fun}{A function that takes the input value and returns a modified
+value. The returned value will be used for the test snapshot.}
+
+\item{session}{A Shiny session object.}
+}
+\description{
+Add a function for serializing an input before bookmarking application state
+}
+\keyword{internal}