diff --git a/PBGitCommitController.h b/PBGitCommitController.h
index 575b17e..31f3419 100644
--- a/PBGitCommitController.h
+++ b/PBGitCommitController.h
@@ -41,6 +41,8 @@
 - (void) readUnstagedFiles:(NSNotification *)notification;
 - (void) stageHunk: (NSString *)hunk reverse:(BOOL)reverse;
 
+- (NSString *)parentTree;
+
 - (IBAction) refresh:(id) sender;
 - (IBAction) commit:(id) sender;
 @end
diff --git a/PBGitIndexController.m b/PBGitIndexController.m
index e56e553..45ca2a7 100644
--- a/PBGitIndexController.m
+++ b/PBGitIndexController.m
@@ -85,7 +85,7 @@
 	if (file.status == NEW)
 		return [commitController.repository outputForArguments:[NSArray arrayWithObjects:@"show", indexPath, nil]];
 
-	return [commitController.repository outputInWorkdirForArguments:[NSArray arrayWithObjects:@"diff", file.commitBlobSHA, indexPath, nil]];
+	return [commitController.repository outputInWorkdirForArguments:[NSArray arrayWithObjects:@"diff-index", @"-p", @"--cached", [commitController parentTree], @"--", file.path, nil]];
 }
 
 - (NSString *)unstagedChangesForFile:(PBChangedFile *)file