diff --git a/R/source.R b/R/source.R
index fc9124d5..6176c7f2 100644
--- a/R/source.R
+++ b/R/source.R
@@ -154,6 +154,7 @@ the$count <- 0L
 generate_cpp_name <- function(name, loaded_dlls = c("cpp11", names(getLoadedDLLs()))) {
   ext <- tools::file_ext(name)
   root <- tools::file_path_sans_ext(basename(name))
+  root <- gsub("[^[:alnum:]_]", "_", root)
   count <- 2
   new_name <- root
   while(new_name %in% loaded_dlls) {
diff --git a/tests/testthat/test-source.R b/tests/testthat/test-source.R
index 2945d51d..c8c60b2b 100644
--- a/tests/testthat/test-source.R
+++ b/tests/testthat/test-source.R
@@ -218,6 +218,24 @@ test_that("cpp_source(d) functions work after sourcing file more than once", {
   expect_equal(foo(), 1)
 })
 
+test_that("cpp_source() cleans file name (#248)", {
+  code <- "
+#include <cpp11.hpp>
+
+[[cpp11::register]]
+int some_function() {return 42; }
+"
+  temp1 <- withr::local_tempfile(fileext = "contains-hyphen.cpp")
+  write(code, temp1)
+  expect_error(cpp11::cpp_source(temp1), NA)
+  expect_equal(some_function(), 42L)
+
+  temp2 <- withr::local_tempfile(fileext = "contains+plus.cpp")
+  write(code, temp2)
+  expect_error(cpp11::cpp_source(temp2), NA)
+  expect_equal(some_function(), 42L)
+})
+
 test_that("cpp_source fails informatively for nonexistent file", {
   i_do_not_exist <- tempfile(pattern = "nope-", fileext = ".cpp")
   expect_false(file.exists(i_do_not_exist))