diff --git a/NEWS.md b/NEWS.md
index 1fe466c..ff1e464 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -5,6 +5,7 @@ the inclusion of IV NCA parameters and additional specifications of
 the dosing including dose amount and route.
 
 # PKNCA 0.11.0.9000
+
 * PKNCA will now give an error when there are unexpected interval columns.
   The `keep_interval_cols` option can be used to mitigate this error.
 * PKNCA will now make verifications on the `intervals` object within the
@@ -17,6 +18,7 @@ the dosing including dose amount and route.
   error.  (#298)
 * Removed native pipes (`|>`) so that PKNCA will work with older versions of R
   (#304).
+* Missing dosing times to `pk.calc.c0()` will not cause an error (#344)
 
 # PKNCA 0.11.0
 
diff --git a/R/pk.calc.c0.R b/R/pk.calc.c0.R
index c39064e..7ea77ba 100644
--- a/R/pk.calc.c0.R
+++ b/R/pk.calc.c0.R
@@ -24,11 +24,15 @@ pk.calc.c0 <- function(conc, time, time.dose=0,
   if (check) {
     assert_conc_time(conc = conc, time = time)
   }
-  if (length(time.dose) != 1)
+  if (length(time.dose) != 1) {
     stop("time.dose must be a scalar")
-  if (!is.numeric(time.dose) | is.factor(time.dose))
+  } else if (!is.numeric(time.dose) | is.factor(time.dose)) {
     stop("time.dose must be a number")
-  if (time.dose > max(time)) {
+  }
+  if (is.na(time.dose)) {
+    warning("time.dose is NA")
+    return(NA)
+  } else if (time.dose > max(time)) {
     warning("time.dose is after all available data")
     return(NA)
   }
diff --git a/tests/testthat/test-pk.calc.c0.R b/tests/testthat/test-pk.calc.c0.R
index adf1146..da0720d 100644
--- a/tests/testthat/test-pk.calc.c0.R
+++ b/tests/testthat/test-pk.calc.c0.R
@@ -11,6 +11,10 @@ test_that("pk.calc.c0", {
   expect_error(pk.calc.c0(5:1, 0:4, method="blah"),
                regexp="should be one of",
                info="method must be valid")
+  expect_warning(
+    pk.calc.c0(conc = 0:3, time = 0:3, time.dose = NA_real_),
+    regexp = "time.dose is NA"
+  )
   expect_warning(pk.calc.c0(5:1, 0:4, time.dose=30),
                  regexp="time.dose is after all available data")