diff --git a/ClangFormat/NSDocument+TRVSClangFormat.m b/ClangFormat/NSDocument+TRVSClangFormat.m
index 51b5128..68f863e 100644
--- a/ClangFormat/NSDocument+TRVSClangFormat.m
+++ b/ClangFormat/NSDocument+TRVSClangFormat.m
@@ -57,7 +57,7 @@ - (BOOL)trvs_shouldFormatBeforeSaving {
 }
 
 - (BOOL)trvs_shouldFormat {
-    return [[NSSet setWithObjects:@"c", @"h", @"cpp", @"cc", @"cxx", @"hh", @"hpp", @"ipp", @"m", @"mm", @"metal", nil] containsObject:[[[self fileURL] pathExtension] lowercaseString]];
+    return [[NSSet setWithObjects:@"c", @"h", @"cpp", @"cc", @"cxx", @"hh", @"hpp", @"hxx", @"ipp", @"m", @"mm", @"metal", nil] containsObject:[[[self fileURL] pathExtension] lowercaseString]];
 }
 
 @end