diff --git a/README.md b/README.md
index 693a0b6..30bbf73 100644
--- a/README.md
+++ b/README.md
@@ -46,6 +46,6 @@ In development, most functionality is currently missing, incomplete, or broken.
    Unicode file names are handled; these are bugs, so please report any issues
    of this type.
 
-3. When reading headers, object IDs are always loaded from `index` lines,
-   regardless of their length. Git calls these fields `{new,old}_oid_prefix`
-   but appears to only load full-length OIDs, ignoring abbreviations.
+3. When reading headers, this library does not validate that OIDs present on an
+   `index` line are shorter than or equal to the maximum hash length, as this
+   requires knowing if the repository used SHA1 or SHA256 hashes.
diff --git a/gitdiff/file_header.go b/gitdiff/file_header.go
index f5711e4..9437f56 100644
--- a/gitdiff/file_header.go
+++ b/gitdiff/file_header.go
@@ -161,13 +161,17 @@ func parseGitHeaderScore(f *File, line, defaultName string) error {
 func parseGitHeaderIndex(f *File, line, defaultName string) error {
 	const sep = ".."
 
+	// note that git stops parsing if the OIDs are too long to be valid
+	// checking this requires knowing if the repository uses SHA1 or SHA256
+	// hashes, which we don't know, so we just skip that check
+
 	parts := strings.SplitN(line, " ", 2)
 	oids := strings.SplitN(parts[0], sep, 2)
 
 	if len(oids) < 2 {
 		return fmt.Errorf("invalid index line: missing %q", sep)
 	}
-	f.OldOID, f.NewOID = oids[0], oids[1]
+	f.OldOIDPrefix, f.NewOIDPrefix = oids[0], oids[1]
 
 	if len(parts) > 1 {
 		return parseGitHeaderOldMode(f, parts[1], defaultName)
diff --git a/gitdiff/file_header_test.go b/gitdiff/file_header_test.go
index e102908..646d739 100644
--- a/gitdiff/file_header_test.go
+++ b/gitdiff/file_header_test.go
@@ -291,24 +291,24 @@ func TestParseGitHeaderData(t *testing.T) {
 		"indexFullSHA1AndMode": {
 			Line: "index 79c6d7f7b7e76c75b3d238f12fb1323f2333ba14..04fab916d8f938173cbb8b93469855f0e838f098 100644\n",
 			OutputFile: &File{
-				OldOID:  "79c6d7f7b7e76c75b3d238f12fb1323f2333ba14",
-				NewOID:  "04fab916d8f938173cbb8b93469855f0e838f098",
-				OldMode: os.FileMode(0100644),
+				OldOIDPrefix: "79c6d7f7b7e76c75b3d238f12fb1323f2333ba14",
+				NewOIDPrefix: "04fab916d8f938173cbb8b93469855f0e838f098",
+				OldMode:      os.FileMode(0100644),
 			},
 		},
 		"indexFullSHA1NoMode": {
 			Line: "index 79c6d7f7b7e76c75b3d238f12fb1323f2333ba14..04fab916d8f938173cbb8b93469855f0e838f098\n",
 			OutputFile: &File{
-				OldOID: "79c6d7f7b7e76c75b3d238f12fb1323f2333ba14",
-				NewOID: "04fab916d8f938173cbb8b93469855f0e838f098",
+				OldOIDPrefix: "79c6d7f7b7e76c75b3d238f12fb1323f2333ba14",
+				NewOIDPrefix: "04fab916d8f938173cbb8b93469855f0e838f098",
 			},
 		},
 		"indexAbbrevSHA1AndMode": {
 			Line: "index 79c6d7..04fab9 100644\n",
 			OutputFile: &File{
-				OldOID:  "79c6d7",
-				NewOID:  "04fab9",
-				OldMode: os.FileMode(0100644),
+				OldOIDPrefix: "79c6d7",
+				NewOIDPrefix: "04fab9",
+				OldMode:      os.FileMode(0100644),
 			},
 		},
 		"indexInvalid": {
diff --git a/gitdiff/gitdiff.go b/gitdiff/gitdiff.go
index c41e6f4..cea3a89 100644
--- a/gitdiff/gitdiff.go
+++ b/gitdiff/gitdiff.go
@@ -18,9 +18,9 @@ type File struct {
 	OldMode os.FileMode
 	NewMode os.FileMode
 
-	OldOID string
-	NewOID string
-	Score  int
+	OldOIDPrefix string
+	NewOIDPrefix string
+	Score        int
 
 	Fragments []*Fragment
 }