diff --git a/plan/builders.go b/plan/builders.go
index f90574d..dbba96a 100644
--- a/plan/builders.go
+++ b/plan/builders.go
@@ -188,7 +188,7 @@ func (b *builder) ProjectRemap(input Rel, remap []int32, exprs ...expr.Expressio
 		return nil, fmt.Errorf("%w: must provide at least one expression for project relation", substraitgo.ErrInvalidRel)
 	}
 
-	noutput := int32(len(input.Remap(input.RecordType()).Types))
+	noutput := int32(len(input.Remap(input.RecordType()).Types) + len(exprs))
 	for _, idx := range remap {
 		if idx < 0 || idx >= noutput {
 			return nil, errOutputMappingOutOfRange
@@ -228,7 +228,7 @@ func (b *builder) AggregateColumnsRemap(input Rel, remap []int32, measures []Agg
 		exprs[i] = []expr.Expression{ref}
 	}
 
-	noutput := int32(len(input.Remap(input.RecordType()).Types))
+	noutput := int32(len(measures) + len(groupByCols))
 	for _, idx := range remap {
 		if idx < 0 || idx >= noutput {
 			return nil, errOutputMappingOutOfRange
@@ -263,7 +263,7 @@ func (b *builder) AggregateExprsRemap(input Rel, remap []int32, measures []AggRe
 		return nil, fmt.Errorf("%w: groupings cannot contain empty expression list or nil expression", substraitgo.ErrInvalidRel)
 	}
 
-	noutput := int32(len(input.Remap(input.RecordType()).Types))
+	noutput := int32(len(measures) + len(groups))
 	for _, idx := range remap {
 		if idx < 0 || idx >= noutput {
 			return nil, errOutputMappingOutOfRange
diff --git a/plan/plan_builder_test.go b/plan/plan_builder_test.go
index 5cd0a58..d5c5ff9 100644
--- a/plan/plan_builder_test.go
+++ b/plan/plan_builder_test.go
@@ -163,8 +163,8 @@ func TestAggregateRelPlan(t *testing.T) {
 							"groupings": [
 								{
 									"groupingExpressions": [
-										{ 
-											"selection": { 
+										{
+											"selection": {
 												"rootReference": {},
 												"directReference": { "structField": { "field": 0 }}
 											}
@@ -185,7 +185,7 @@ func TestAggregateRelPlan(t *testing.T) {
 										"invocation": "AGGREGATION_INVOCATION_ALL"
 									}
 								}
-							]							
+							]
 						}
 					},
 					"names": ["val", "cnt"]
@@ -264,6 +264,16 @@ func TestAggregateRelErrors(t *testing.T) {
 	_, err = b.AggregateExprsRemap(scan, []int32{5, -1}, nil, []expr.Expression{ref})
 	assert.ErrorIs(t, err, substraitgo.ErrInvalidRel)
 	assert.ErrorContains(t, err, "output mapping index out of range")
+
+	_, err = b.AggregateExprsRemap(scan, []int32{1}, nil, []expr.Expression{ref})
+	assert.ErrorIs(t, err, substraitgo.ErrInvalidRel)
+	assert.ErrorContains(t, err, "output mapping index out of range")
+
+	_, err = b.AggregateExprsRemap(scan, []int32{0}, nil, []expr.Expression{ref})
+	assert.NoError(t, err)
+	_, err = b.AggregateColumnsRemap(scan, []int32{0}, nil, 0)
+	assert.NoError(t, err)
+
 }
 
 func TestCrossRel(t *testing.T) {
@@ -357,10 +367,14 @@ func TestCrossRelErrors(t *testing.T) {
 	_, err = b.CrossRemap(left, right, []int32{5})
 	assert.ErrorIs(t, err, substraitgo.ErrInvalidRel)
 	assert.ErrorContains(t, err, "output mapping index out of range")
+
+	// Output is length 2 + 2
+	_, err = b.CrossRemap(left, right, []int32{2, 3})
+	assert.NoError(t, err)
 }
 
 func TestFetchRel(t *testing.T) {
-	const expectedJSON = `{	
+	const expectedJSON = `{
 		` + versionStruct + `,
 		"relations": [
 			{
@@ -895,7 +909,7 @@ func TestSortRelationKeyEqual(t *testing.T) {
 
 func TestSortRelationMultiple(t *testing.T) {
 	const expectedJSON = `{
-		` + versionStruct + `,		
+		` + versionStruct + `,
 		"relations": [
 			{
 				"root": {
@@ -1135,6 +1149,9 @@ func TestProjectErrors(t *testing.T) {
 	_, err = b.ProjectRemap(scan, []int32{3}, ref)
 	assert.ErrorIs(t, err, substraitgo.ErrInvalidRel)
 	assert.ErrorContains(t, err, "output mapping index out of range")
+
+	_, err = b.ProjectRemap(scan, []int32{2}, ref)
+	assert.NoError(t, err, "Expected expression mapping to be in-bounds")
 }
 
 func TestSetRelations(t *testing.T) {