diff --git a/NEWS.md b/NEWS.md
index 7aeb2497ce..10816c1353 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -299,6 +299,8 @@
 
 18. Added a note to `?setkey` clarifying that `setkey` always uses C-locale sorting (as has been noted in `?setorder`). Thanks @JBreidaks for the report in [#2114](https://github.com/Rdatatable/data.table/issues/2114).
 
+19. `hour()`/`minute()`/`second()` are much faster for `ITime` input, [#3518](https://github.com/Rdatatable/data.table/issues/3158).
+
 
 ### Changes in [v1.12.2](https://github.com/Rdatatable/data.table/milestone/14?closed=1)  (07 Apr 2019)
 
diff --git a/R/IDateTime.R b/R/IDateTime.R
index c0e31bc248..3c28fa909f 100644
--- a/R/IDateTime.R
+++ b/R/IDateTime.R
@@ -303,28 +303,22 @@ as.POSIXlt.ITime = function(x, ...) {
 ###################################################################
 
 second  = function(x) {
-  if (inherits(x, 'POSIXct') && identical(attr(x, 'tzone', exact=TRUE), 'UTC')) {
-    # if we know the object is in UTC, can calculate the hour much faster
-    as.integer(as.numeric(x) %% 60L)
-  } else {
-    as.integer(as.POSIXlt(x)$sec)
-  }
+  # if we know the object is in UTC, can calculate the hour much faster
+  if (inherits(x, 'POSIXct') && identical(attr(x, 'tzone', exact=TRUE), 'UTC')) return(as.integer(as.numeric(x) %% 60L))
+  if (inherits(x, 'ITime')) return(as.integer(x) %% 60L)
+  as.integer(as.POSIXlt(x)$sec)
 }
 minute  = function(x) {
-  if (inherits(x, 'POSIXct') && identical(attr(x, 'tzone', exact=TRUE), 'UTC')) {
-    # ever-so-slightly faster than x %% 3600L %/% 60L
-    as.integer(as.numeric(x) %/% 60L %% 60L)
-  } else {
-    as.POSIXlt(x)$min
-  }
+  # ever-so-slightly faster than x %% 3600L %/% 60L
+  if (inherits(x, 'POSIXct') && identical(attr(x, 'tzone', exact=TRUE), 'UTC')) return(as.integer(as.numeric(x) %/% 60L %% 60L))
+  if (inherits(x, 'ITime')) return(as.integer(x) %/% 60L %% 60L)
+  as.POSIXlt(x)$min
 }
 hour = function(x) {
-  if (inherits(x, 'POSIXct') && identical(attr(x, 'tzone', exact=TRUE), 'UTC')) {
-    # ever-so-slightly faster than x %% 86400L %/% 3600L
-    as.integer(as.numeric(x) %/% 3600L %% 24L)
-  } else {
-    as.POSIXlt(x)$hour
-  }
+  # ever-so-slightly faster than x %% 86400L %/% 3600L
+  if (inherits(x, 'POSIXct') && identical(attr(x, 'tzone', exact=TRUE), 'UTC')) return(as.integer(as.numeric(x) %/% 3600L %% 24L))
+  if (inherits(x, 'ITime')) return(as.integer(x) %/% 3600L %% 24L)
+  as.POSIXlt(x)$hour
 }
 yday    = function(x) as.POSIXlt(x)$yday + 1L
 wday    = function(x) (unclass(as.IDate(x)) + 4L) %% 7L + 1L
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index c9067a2b42..8c72cf6c29 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -13361,6 +13361,10 @@ z = .POSIXct(3725, 'UTC')
 test(1962.101, second(z), 5L)
 test(1962.102, minute(z), 2L)
 test(1962.103, hour(z), 1L)
+z = as.ITime(z)
+test(1962.201, second(z), 5L)
+test(1962.202, minute(z), 2L)
+test(1962.203, hour(z), 1L)
 
 # positive and negative values for shift, #1708
 DT = data.table(x = 1:10, y = 10:1)