diff --git a/src/gn/source_file.cc b/src/gn/source_file.cc
index 319adde..3a9198b 100644
--- a/src/gn/source_file.cc
+++ b/src/gn/source_file.cc
@@ -101,6 +101,9 @@
   }
 
   // Other cases
+  if (EndsWithExtension(file, "hpp11"))
+    return SourceFile::SOURCE_H;
+
   if (EndsWithExtension(file, "swift"))
     return SourceFile::SOURCE_SWIFT;
 
diff --git a/src/gn/source_file_unittest.cc b/src/gn/source_file_unittest.cc
index 6c409b1..998fae4 100644
--- a/src/gn/source_file_unittest.cc
+++ b/src/gn/source_file_unittest.cc
@@ -33,6 +33,7 @@
       {"foo.h", SourceFile::SOURCE_H},
       {"foo.hh", SourceFile::SOURCE_H},
       {"foo.hpp", SourceFile::SOURCE_H},
+      {"foo.hpp11", SourceFile::SOURCE_H},
       {"foo.inc", SourceFile::SOURCE_H},
       {"foo.inl", SourceFile::SOURCE_H},
       {"foo.ipp", SourceFile::SOURCE_H},