diff --git a/src/builtins/core/date.rs b/src/builtins/core/date.rs
index f9a6a53b9..8819c3a34 100644
--- a/src/builtins/core/date.rs
+++ b/src/builtins/core/date.rs
@@ -7,7 +7,7 @@ use crate::{
     iso::{IsoDate, IsoDateTime, IsoTime},
     options::{
         ArithmeticOverflow, DifferenceOperation, DifferenceSettings, DisplayCalendar,
-        ResolvedRoundingOptions, TemporalUnit,
+        ResolvedRoundingOptions, TemporalUnit, UnitGroup,
     },
     parsers::{parse_date_time, IxdtfStringBuilder},
     primitive::FiniteF64,
@@ -253,6 +253,7 @@ impl PlainDate {
         let resolved = ResolvedRoundingOptions::from_diff_settings(
             settings,
             op,
+            UnitGroup::Date,
             TemporalUnit::Day,
             TemporalUnit::Day,
         )?;
diff --git a/src/builtins/core/datetime.rs b/src/builtins/core/datetime.rs
index 62709afbf..6073b5a7f 100644
--- a/src/builtins/core/datetime.rs
+++ b/src/builtins/core/datetime.rs
@@ -9,7 +9,7 @@ use crate::{
     iso::{IsoDate, IsoDateTime, IsoTime},
     options::{
         ArithmeticOverflow, DifferenceOperation, DifferenceSettings, DisplayCalendar,
-        ResolvedRoundingOptions, RoundingOptions, TemporalUnit, ToStringRoundingOptions,
+        ResolvedRoundingOptions, RoundingOptions, TemporalUnit, ToStringRoundingOptions, UnitGroup,
     },
     parsers::{parse_date_time, IxdtfStringBuilder},
     provider::NeverProvider,
@@ -121,6 +121,7 @@ impl PlainDateTime {
         let options = ResolvedRoundingOptions::from_diff_settings(
             settings,
             op,
+            UnitGroup::DateTime,
             TemporalUnit::Day,
             TemporalUnit::Nanosecond,
         )?;
diff --git a/src/builtins/core/instant.rs b/src/builtins/core/instant.rs
index 7726358ae..548fd50d8 100644
--- a/src/builtins/core/instant.rs
+++ b/src/builtins/core/instant.rs
@@ -10,7 +10,7 @@ use crate::{
     iso::IsoDateTime,
     options::{
         DifferenceOperation, DifferenceSettings, DisplayOffset, ResolvedRoundingOptions,
-        RoundingOptions, TemporalUnit, ToStringRoundingOptions,
+        RoundingOptions, TemporalUnit, ToStringRoundingOptions, UnitGroup,
     },
     parsers::{parse_instant, IxdtfStringBuilder},
     primitive::FiniteF64,
@@ -88,6 +88,7 @@ impl Instant {
         let resolved_options = ResolvedRoundingOptions::from_diff_settings(
             options,
             op,
+            UnitGroup::Time,
             TemporalUnit::Second,
             TemporalUnit::Nanosecond,
         )?;
diff --git a/src/builtins/core/time.rs b/src/builtins/core/time.rs
index 349b2d2fa..ee8ae3c71 100644
--- a/src/builtins/core/time.rs
+++ b/src/builtins/core/time.rs
@@ -5,7 +5,7 @@ use crate::{
     iso::IsoTime,
     options::{
         ArithmeticOverflow, DifferenceOperation, DifferenceSettings, ResolvedRoundingOptions,
-        RoundingIncrement, TemporalRoundingMode, TemporalUnit, ToStringRoundingOptions,
+        RoundingIncrement, TemporalRoundingMode, TemporalUnit, ToStringRoundingOptions, UnitGroup,
     },
     parsers::{parse_time, IxdtfStringBuilder},
     primitive::FiniteF64,
@@ -127,6 +127,7 @@ impl PlainTime {
         let resolved = ResolvedRoundingOptions::from_diff_settings(
             settings,
             op,
+            UnitGroup::Time,
             TemporalUnit::Hour,
             TemporalUnit::Nanosecond,
         )?;
diff --git a/src/builtins/core/zoneddatetime.rs b/src/builtins/core/zoneddatetime.rs
index c2ad3eb31..a7b32fb5b 100644
--- a/src/builtins/core/zoneddatetime.rs
+++ b/src/builtins/core/zoneddatetime.rs
@@ -17,7 +17,7 @@ use crate::{
         ArithmeticOverflow, DifferenceOperation, DifferenceSettings, Disambiguation,
         DisplayCalendar, DisplayOffset, DisplayTimeZone, OffsetDisambiguation,
         ResolvedRoundingOptions, RoundingIncrement, TemporalRoundingMode, TemporalUnit,
-        ToStringRoundingOptions,
+        ToStringRoundingOptions, UnitGroup,
     },
     parsers::{self, FormattableOffset, FormattableTime, IxdtfStringBuilder, Precision},
     partial::{PartialDate, PartialTime},
@@ -259,6 +259,7 @@ impl ZonedDateTime {
         let resolved_options = ResolvedRoundingOptions::from_diff_settings(
             options,
             op,
+            UnitGroup::DateTime,
             TemporalUnit::Hour,
             TemporalUnit::Nanosecond,
         )?;
diff --git a/src/options.rs b/src/options.rs
index 6b21468e5..09c793d84 100644
--- a/src/options.rs
+++ b/src/options.rs
@@ -177,11 +177,13 @@ impl ResolvedRoundingOptions {
     pub(crate) fn from_diff_settings(
         options: DifferenceSettings,
         operation: DifferenceOperation,
+        unit_group: UnitGroup,
         fallback_largest: TemporalUnit,
         fallback_smallest: TemporalUnit,
     ) -> TemporalResult<Self> {
         // 4. Let resolvedOptions be ? SnapshotOwnProperties(? GetOptionsObject(options), null).
         // 5. Let settings be ? GetDifferenceSettings(operation, resolvedOptions, DATE, « », "day", "day").
+        unit_group.validate_unit(options.largest_unit)?;
         let increment = options.increment.unwrap_or_default();
         let rounding_mode = match operation {
             DifferenceOperation::Since => options
@@ -341,6 +343,33 @@ impl ResolvedRoundingOptions {
 
 // ==== Options enums and methods ====
 
+pub enum UnitGroup {
+    Date,
+    Time,
+    DateTime,
+}
+
+impl UnitGroup {
+    pub fn validate_unit(self, unit: Option<TemporalUnit>) -> TemporalResult<()> {
+        // TODO: Determine proper handling of Auto.
+        match self {
+            UnitGroup::Date => match unit {
+                Some(unit) if !unit.is_time_unit() => Ok(()),
+                None => Ok(()),
+                _ => Err(TemporalError::range()
+                    .with_message("Unit was not part of the date unit group.")),
+            },
+            UnitGroup::Time => match unit {
+                Some(unit) if unit.is_time_unit() => Ok(()),
+                None => Ok(()),
+                _ => Err(TemporalError::range()
+                    .with_message("Unit was not part of the time unit group.")),
+            },
+            UnitGroup::DateTime => Ok(()),
+        }
+    }
+}
+
 /// The relevant unit that should be used for the operation that
 /// this option is provided as a value.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]