diff --git a/spark/src/main/scala/org/apache/comet/serde/aggregates.scala b/spark/src/main/scala/org/apache/comet/serde/aggregates.scala
index bb0466b4eb..e6e32ebbc5 100644
--- a/spark/src/main/scala/org/apache/comet/serde/aggregates.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/aggregates.scala
@@ -205,8 +205,6 @@ object CometAverage extends CometAggregateExpressionSerde[Average] {
 
 object CometSum extends CometAggregateExpressionSerde[Sum] {
 
-  override def getIncompatibleReasons(): Seq[String] = Seq("Falls back to Spark in ANSI mode.")
-
   override def convert(
       aggExpr: AggregateExpression,
       sum: Sum,
diff --git a/spark/src/main/scala/org/apache/comet/serde/strings.scala b/spark/src/main/scala/org/apache/comet/serde/strings.scala
index 968fe8cd69..4c818f24c6 100644
--- a/spark/src/main/scala/org/apache/comet/serde/strings.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/strings.scala
@@ -33,7 +33,7 @@ import org.apache.comet.serde.QueryPlanSerde.{createBinaryExpr, exprToProtoInter
 
 object CometStringRepeat extends CometExpressionSerde[StringRepeat] {
 
-  override def getCompatibleNotes(): Seq[String] = Seq(
+  override def getIncompatibleReasons(): Seq[String] = Seq(
     "A negative argument for the number of times to repeat throws an exception" +
       " instead of returning an empty string as Spark does")
 
diff --git a/spark/src/main/scala/org/apache/comet/serde/unixtime.scala b/spark/src/main/scala/org/apache/comet/serde/unixtime.scala
index e5eeb5b848..b561c24787 100644
--- a/spark/src/main/scala/org/apache/comet/serde/unixtime.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/unixtime.scala
@@ -29,12 +29,27 @@ import org.apache.comet.serde.QueryPlanSerde.{exprToProtoInternal, optExprWithIn
 // https://github.com/apache/datafusion/issues/16594
 object CometFromUnixTime extends CometExpressionSerde[FromUnixTime] {
 
+  override def getUnsupportedReasons(): Seq[String] = Seq(
+    "Only supports the default datetime format pattern `yyyy-MM-dd HH:mm:ss`")
+
   override def getIncompatibleReasons(): Seq[String] = Seq(
-    "Only supports the default datetime format pattern `yyyy-MM-dd HH:mm:ss`." +
-      " DataFusion's valid timestamp range differs from Spark" +
+    "DataFusion's valid timestamp range differs from Spark" +
       " (https://github.com/apache/datafusion/issues/16594)")
 
-  override def getSupportLevel(expr: FromUnixTime): SupportLevel = Incompatible(None)
+  override def getSupportLevel(expr: FromUnixTime): SupportLevel = {
+    expr.format match {
+      case Literal(fmt, _) =>
+        val formatStr = fmt.toString
+        val defaultPattern = TimestampFormatter.defaultPattern
+        if (formatStr == defaultPattern) {
+          Incompatible(None)
+        } else {
+          Unsupported(Some(s"Datetime pattern format: $formatStr is unsupported"))
+        }
+      case _ =>
+        Unsupported(Some("Non-literal datetime pattern format is unsupported"))
+    }
+  }
 
   override def convert(
       expr: FromUnixTime,
@@ -48,10 +63,7 @@ object CometFromUnixTime extends CometExpressionSerde[FromUnixTime] {
     val formatExpr = exprToProtoInternal(Literal("%Y-%m-%d %H:%M:%S"), inputs, binding)
     val timeZone = exprToProtoInternal(Literal(expr.timeZoneId.orNull), inputs, binding)
 
-    if (expr.format != Literal(TimestampFormatter.defaultPattern)) {
-      withInfo(expr, "Datetime pattern format is unsupported")
-      None
-    } else if (secExpr.isDefined && formatExpr.isDefined) {
+    if (secExpr.isDefined && formatExpr.isDefined) {
       val timestampExpr =
         scalarFunctionExprToProto("from_unixtime", Seq(secExpr, timeZone): _*)
       val optExpr = scalarFunctionExprToProto("to_char", Seq(timestampExpr, formatExpr): _*)
diff --git a/spark/src/test/resources/sql-tests/expressions/datetime/from_unix_time.sql b/spark/src/test/resources/sql-tests/expressions/datetime/from_unix_time.sql
index a7b0960570..47c76d67aa 100644
--- a/spark/src/test/resources/sql-tests/expressions/datetime/from_unix_time.sql
+++ b/spark/src/test/resources/sql-tests/expressions/datetime/from_unix_time.sql
@@ -24,12 +24,12 @@ INSERT INTO test_from_unix_time VALUES (0), (1718451045), (-1), (NULL), (2147483
 query expect_fallback(not fully compatible with Spark)
 SELECT from_unixtime(t) FROM test_from_unix_time
 
-query expect_fallback(not fully compatible with Spark)
+query expect_fallback(Datetime pattern format: yyyy-MM-dd is unsupported)
 SELECT from_unixtime(t, 'yyyy-MM-dd') FROM test_from_unix_time
 
 -- literal arguments
 query expect_fallback(not fully compatible with Spark)
 SELECT from_unixtime(0)
 
-query expect_fallback(not fully compatible with Spark)
+query expect_fallback(Datetime pattern format: yyyy-MM-dd is unsupported)
 SELECT from_unixtime(1718451045, 'yyyy-MM-dd')