diff --git a/CHANGELOG.md b/CHANGELOG.md
index 775b0eea3..a75f3e835 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Contacts backups no longer slices root-folder data if outlook is set to languages other than english.
+- Failed backups if the --disable-incrementals flag was passed when there was a valid merge base under some conditions.
 
 ## [v0.12.0] (beta) - 2023-08-29
 
diff --git a/src/internal/kopia/backup_bases.go b/src/internal/kopia/backup_bases.go
index d9e240132..18624236b 100644
--- a/src/internal/kopia/backup_bases.go
+++ b/src/internal/kopia/backup_bases.go
@@ -48,9 +48,6 @@ type backupBases struct {
 	// disableAssistBases denote whether any assist bases should be returned to
 	// kopia during snapshot operation.
 	disableAssistBases bool
-	// disableMergeBases denotes whether any bases should be returned from calls
-	// to MergeBases().
-	disableMergeBases bool
 }
 
 func (bb *backupBases) SnapshotAssistBases() []ManifestEntry {
@@ -99,10 +96,6 @@ func (bb *backupBases) ConvertToAssistBase(manifestID manifest.ID) {
 }
 
 func (bb backupBases) Backups() []BackupEntry {
-	if bb.disableMergeBases {
-		return nil
-	}
-
 	return slices.Clone(bb.backups)
 }
 
@@ -131,15 +124,20 @@ func (bb *backupBases) MinBackupVersion() int {
 }
 
 func (bb backupBases) MergeBases() []ManifestEntry {
-	if bb.disableMergeBases {
-		return nil
-	}
-
 	return slices.Clone(bb.mergeBases)
 }
 
 func (bb *backupBases) DisableMergeBases() {
-	bb.disableMergeBases = true
+	// Turn all merge bases into assist bases. We don't want to remove them
+	// completely because we still want to allow kopia assisted incrementals
+	// unless that's also explicitly disabled. However, we can't just leave them
+	// in the merge set since then we won't return the bases when merging backup
+	// details.
+	bb.assistBases = append(bb.assistBases, bb.mergeBases...)
+	bb.assistBackups = append(bb.assistBackups, bb.backups...)
+
+	bb.mergeBases = nil
+	bb.backups = nil
 }
 
 func (bb backupBases) UniqueAssistBases() []ManifestEntry {
diff --git a/src/internal/kopia/backup_bases_test.go b/src/internal/kopia/backup_bases_test.go
index 7ef16ec13..3ff1488e5 100644
--- a/src/internal/kopia/backup_bases_test.go
+++ b/src/internal/kopia/backup_bases_test.go
@@ -8,6 +8,7 @@ import (
 	"github.com/kopia/kopia/snapshot"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/suite"
+	"golang.org/x/exp/slices"
 
 	"github.com/alcionai/corso/src/internal/model"
 	"github.com/alcionai/corso/src/internal/tester"
@@ -201,10 +202,20 @@ func (suite *BackupBasesUnitSuite) TestConvertToAssistBase() {
 
 func (suite *BackupBasesUnitSuite) TestDisableMergeBases() {
 	t := suite.T()
+
+	merge := []BackupEntry{
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "m1"}}},
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "m2"}}},
+	}
+	assist := []BackupEntry{
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "a1"}}},
+		{Backup: &backup.Backup{BaseModel: model.BaseModel{ID: "a2"}}},
+	}
+
 	bb := &backupBases{
-		backups:       make([]BackupEntry, 2),
+		backups:       slices.Clone(merge),
 		mergeBases:    make([]ManifestEntry, 2),
-		assistBackups: make([]BackupEntry, 2),
+		assistBackups: slices.Clone(assist),
 		assistBases:   make([]ManifestEntry, 2),
 	}
 
@@ -212,12 +223,15 @@ func (suite *BackupBasesUnitSuite) TestDisableMergeBases() {
 	assert.Empty(t, bb.Backups())
 	assert.Empty(t, bb.MergeBases())
 
-	// Assist base set should be unchanged.
-	assert.Len(t, bb.UniqueAssistBackups(), 2)
-	assert.Len(t, bb.UniqueAssistBases(), 2)
-	// Merge bases should still appear in the assist base set passed in for kopia
-	// snapshots.
+	// Assist base set now has what used to be merge bases.
+	assert.Len(t, bb.UniqueAssistBases(), 4)
 	assert.Len(t, bb.SnapshotAssistBases(), 4)
+	// Merge bases should appear in the set of backup bases used for details
+	// merging.
+	assert.ElementsMatch(
+		t,
+		append(slices.Clone(merge), assist...),
+		bb.UniqueAssistBackups())
 }
 
 func (suite *BackupBasesUnitSuite) TestDisableAssistBases() {
diff --git a/src/internal/model/model.go b/src/internal/model/model.go
index fb72e3613..0bb73d321 100644
--- a/src/internal/model/model.go
+++ b/src/internal/model/model.go
@@ -36,8 +36,23 @@ const (
 const (
 	ServiceTag    = "service"
 	BackupTypeTag = "backup-type"
-	AssistBackup  = "assist-backup"
-	MergeBackup   = "merge-backup"
+	// AssistBackup denotes that this backup should only be used for kopia
+	// assisted incrementals since it doesn't contain the complete set of data
+	// being backed up.
+	//
+	// This tag should only be used for finding backups during a
+	// manifest search. It shouldn't be used to differentiate between backups once
+	// the manifest search completes.
+	AssistBackup = "assist-backup"
+	// MergeBackup denotes that this backup can be used as a merge base during an
+	// incremental backup. It contains a complete snapshot of the data in the
+	// external service. Merge bases can also be used as assist bases during an
+	// incremental backup or demoted to being only an assist base.
+	//
+	// This tag should only be used for finding backups during a
+	// manifest search. It shouldn't be used to differentiate between backups once
+	// the manifest search completes.
+	MergeBackup = "merge-backup"
 )
 
 // Valid returns true if the ModelType value fits within the const range.