diff --git a/NEWS.md b/NEWS.md
index c0eda5f..184951c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,10 @@
 # tibbletime (development version)
 
+* Bug fixes
+
+    * `collapse_by()` no longer errors when there is a column 
+    named `start_date` in the `tbl_time` object (#81).
+
 ## tibbletime 0.1.2
 
 * Features
diff --git a/R/collapse_index.R b/R/collapse_index.R
index 7a56c17..c0659e7 100644
--- a/R/collapse_index.R
+++ b/R/collapse_index.R
@@ -187,12 +187,14 @@ collapse_by <- function(.tbl_time, period = "yearly", start_date = NULL, side =
   index_quo  <- get_index_quo(.tbl_time)
   index_char <- get_index_char(.tbl_time)
 
+  start_date <- rlang::enquo(start_date)
+
   .tbl_time_collapsed <- dplyr::mutate(
     .data = .tbl_time,
     !! index_char := collapse_index(
       index      = !! index_quo,
       period     = period,
-      start_date = start_date,
+      start_date = !! start_date,
       side       = side,
       clean      = clean,
       ...
diff --git a/tests/testthat/test_collapse_index.R b/tests/testthat/test_collapse_index.R
index 885165a..46c03fe 100644
--- a/tests/testthat/test_collapse_index.R
+++ b/tests/testthat/test_collapse_index.R
@@ -63,3 +63,29 @@ test_that("day becomes DSTday for POSIXct to prevent DST boundary problems", {
 
   expect_equal(ret, test)
 })
+
+test_that("can use `collapse_by()` when a column is named `start_date` (#81)", {
+  x <- data.frame(
+    start_date = as.Date("2017-12-01") + 0:2,
+    value  = c(1, 2, 3)
+  )
+
+  x <- as_tbl_time(x, start_date)
+
+  expect_equal(
+    collapse_by(x),
+    dplyr::mutate(x, start_date = collapse_index(start_date))
+  )
+
+  expect_equal(
+    collapse_by(x, start_date = as.Date("2017-01-01"), side = "start", period = "2 days"),
+    dplyr::mutate(x, start_date = collapse_index(start_date, "2 days", start_date = as.Date("2017-01-01"), side = "start"))
+  )
+
+  expect_equal(
+    collapse_by(x, start_date = as.Date("2016-12-31"), side = "start", period = "2 days"),
+    dplyr::mutate(x, start_date = collapse_index(start_date, "2 days", start_date = as.Date("2016-12-31"), side = "start"))
+  )
+})
+
+