diff --git a/R/read_csv.R b/R/read_csv.R
index 6021e637b..2fd6cc057 100644
--- a/R/read_csv.R
+++ b/R/read_csv.R
@@ -203,9 +203,14 @@ read_cmdstan_csv <- function(files,
     } else if (metadata$method == "optimize") {
       all_draws <- 1
     }
+    if (os_is_windows()) {
+      fread_cmd <- paste0("findstr /b /v '#' ", output_file)
+    } else {
+      fread_cmd <- paste0("grep -v '^#' ", output_file)
+    }
     suppressWarnings(
       draws <- data.table::fread(
-        cmd = paste0("grep -v '^#' ", output_file),
+        cmd = fread_cmd,
         select = col_select
       )
     )
@@ -380,9 +385,14 @@ read_csv_metadata <- function(csv_file) {
   csv_file_info <- list()
   inv_metric_rows <- 0
   parsing_done <- FALSE
+  if (os_is_windows()) {
+    fread_cmd <- paste0("findstr /b /v '[#a-zA-Z]' ", output_file)
+  } else {
+    fread_cmd <- paste0("grep -v '^#' ", output_file)
+  }
   suppressWarnings(
     metadata <- data.table::fread(
-      cmd = paste0("grep '^[#a-zA-Z]' ", csv_file),
+      cmd = fread_cmd,
       colClasses = "character",
       stringsAsFactors = FALSE,
       fill = TRUE,