diff --git a/examples/time.roc b/examples/time.roc
index adf6325a..02e50bf6 100644
--- a/examples/time.roc
+++ b/examples/time.roc
@@ -14,8 +14,7 @@ main! = |_args| {
 
 	Stdout.line!("Started at ${Utc.to_iso_8601(start)}")?
 
-	# 1000 ms = 1 second
-	Sleep.millis!(1000)
+	Sleep.seconds!(1)
 
 	finish : U128
 	finish = Utc.now!()
diff --git a/platform/Sleep.roc b/platform/Sleep.roc
index a147a951..816c15be 100644
--- a/platform/Sleep.roc
+++ b/platform/Sleep.roc
@@ -1,9 +1,44 @@
 import Host
 
+## Convert a duration in seconds into whole milliseconds for the host.
+##
+## `to_u64_try` rejects negative, `NaN`, and too-large values alike, so a
+## positive value here is one that overflowed the millisecond range.
+millis_from_seconds : F64 -> U64
+millis_from_seconds = |seconds|
+	match F64.to_u64_try(seconds * 1000) {
+		Ok(milliseconds) => milliseconds
+		Err(OutOfRange) => if seconds > 0 U64.highest else 0
+	}
+
 ## Pause the current process for a requested duration.
 Sleep :: [].{
 
 	## Sleep for the specified number of milliseconds.
 	millis! : U64 => {}
 	millis! = |milliseconds| Host.sleep_millis!(milliseconds)
+
+	## Sleep for the specified number of seconds.
+	##
+	## The duration is truncated to whole milliseconds, so `Sleep.seconds!(1.5)`
+	## sleeps for 1500 ms. Negative and `NaN` durations return immediately, and
+	## durations past [U64.highest] milliseconds saturate there.
+	seconds! : F64 => {}
+	seconds! = |seconds| Host.sleep_millis!(millis_from_seconds(seconds))
 }
+
+expect millis_from_seconds(1) == 1000
+expect millis_from_seconds(1.5) == 1500
+expect millis_from_seconds(0.25) == 250
+expect millis_from_seconds(0) == 0
+
+# Sub-millisecond durations truncate toward zero rather than rounding up.
+expect millis_from_seconds(0.0004) == 0
+
+# Negative and NaN durations return immediately instead of crashing.
+expect millis_from_seconds(-5) == 0
+expect millis_from_seconds(F64.nan) == 0
+
+# Durations beyond the host's millisecond counter saturate.
+expect millis_from_seconds(F64.infinity) == U64.highest
+expect millis_from_seconds(1.0e30) == U64.highest