diff --git a/PBDiffWindowController.m b/PBDiffWindowController.m
index 06403d5..ae545d9 100644
--- a/PBDiffWindowController.m
+++ b/PBDiffWindowController.m
@@ -34,7 +34,7 @@
 		diffCommit = [startCommit.repository headCommit];
 
 	NSString *commitSelector = [NSString stringWithFormat:@"%@..%@", [startCommit realSha], [diffCommit realSha]];
-	NSMutableArray *arguments = [NSMutableArray arrayWithObjects:@"diff", commitSelector, nil];
+	NSMutableArray *arguments = [NSMutableArray arrayWithObjects:@"diff", @"--no-ext-diff", commitSelector, nil];
 
 	if (![PBGitDefaults showWhitespaceDifferences])
 		[arguments insertObject:@"-w" atIndex:1];
diff --git a/gitx.m b/gitx.m
index 3230d01..8c1ae4e 100644
--- a/gitx.m
+++ b/gitx.m
@@ -124,9 +124,9 @@ void handleSTDINDiff()
 	}
 }
 
-void handleDiffWithArguments(NSURL *repositoryURL, NSMutableArray *arguments)
+void handleDiffWithArguments(NSURL *repositoryURL, NSArray *arguments)
 {
-	[arguments insertObject:@"diff" atIndex:0];
+	arguments = [[NSArray arrayWithObjects:@"diff", @"--no-ext-diff", nil] arrayByAddingObjectsFromArray:arguments];
 
 	int retValue = 1;
 	NSString *diffOutput = [PBEasyPipe outputForCommand:[PBGitBinary path] withArgs:arguments inDir:[repositoryURL path] retValue:&retValue];