diff --git a/R/add_r_files.R b/R/add_r_files.R
index 29fa5108..897d393b 100644
--- a/R/add_r_files.R
+++ b/R/add_r_files.R
@@ -18,9 +18,9 @@ add_r_files <- function(
 		),
 		"pkg"
 	)
-	name <- file_path_sans_ext(
+	name <- sanitize_r_name(file_path_sans_ext(
 		name
-	)
+	))
 
 	check_name_length_is_one(
 		name
@@ -100,17 +100,10 @@ add_r_files <- function(
 			"_"
 		)
 	}
-
-	where <- fs_path(
-		"R",
-		paste0(
-			module,
-			ext,
-			"_",
-			name,
-			".R"
-		)
-	)
+	tmp_name <- paste0(module, ext,  "_", name, ".R")
+	# Only if the fct. name is "".
+	if(name == "" && grepl("_.R$", tmp_name)) tmp_name <- gsub("_.R$", ".R", tmp_name)
+	where <- fs_path("R", tmp_name)
 
 	if (
 		!fs_file_exists(
diff --git a/R/utils.R b/R/utils.R
index baadf0b9..9f620ece 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -331,6 +331,20 @@ check_name_length_is_one <- function(
 	)
 }
 
+# Convert filename to lowercase and replace space/special with underscores
+# Similar to janitor::make_clean_names() but without the dependency
+sanitize_r_name <- function(name) {
+	name <- tolower(name)
+	name <- gsub("[^a-z0-9_]", "_", name)
+	name <- gsub("^_+|_+$", "", name)
+	name <- gsub("_+", "_", name)
+	if (grepl("^[0-9]", name)) {
+		name <- paste0("x", name)
+	}
+	if (name == "" || is.na(name)) name <- ""
+	name
+}
+
 do_if_unquiet <- function(
 	expr
 ) {
diff --git a/tests/testthat/test-add_r_files.R b/tests/testthat/test-add_r_files.R
index 3a798601..fe957b71 100644
--- a/tests/testthat/test-add_r_files.R
+++ b/tests/testthat/test-add_r_files.R
@@ -112,3 +112,70 @@ test_that("add_fct and add_utils", {
 		}
 	)
 })
+
+test_that("add_fct sanitizes names correctly", {
+	run_quietly_in_a_dummy_golem({
+		# Name with spaces
+
+		add_fct(
+			"ma fonction",
+			open = FALSE
+		)
+		expect_exists(
+			file.path(
+				"R",
+				"fct_ma_fonction.R"
+			)
+		)
+
+		# Name with special characters
+
+		add_fct(
+			"my-special@function!",
+			open = FALSE
+		)
+		expect_exists(
+			file.path(
+				"R",
+				"fct_my_special_function.R"
+			)
+		)
+
+		file_content2 <- readLines(
+			file.path(
+				"R",
+				"fct_my_special_function.R"
+			)
+		)
+		expect_true(
+			any(grepl(
+				"my_special_function <- function",
+				file_content2,
+				fixed = TRUE
+			))
+		)
+
+		# Name starting with number
+
+		add_fct(
+			"123function",
+			open = FALSE
+		)
+		expect_exists(
+			file.path(
+				"R",
+				"fct_x123function.R"
+			)
+		)
+
+		file_content3 <- readLines(
+			file.path(
+				"R",
+				"fct_x123function.R"
+			)
+		)
+		expect_true(
+			any(grepl("x123function <- function", file_content3, fixed = TRUE))
+		)
+	})
+})